HS-ETS1-3: Evaluating Solutions with Prioritized Criteria and Trade-offs
In plain English: HS-ETS1-3 is the NGSS high school performance expectation that asks students to evaluate a solution to a complex real-world problem using prioritized criteria and trade-offs. Students weigh cost, safety, reliability and aesthetics along with social, cultural and environmental impacts, and justify a choice with evidence. It is usually taught inside a high school science or engineering course.
Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics, as well as possible social, cultural, and environmental impacts.
Next Generation Science Standards · Disciplinary Core Idea: Engineering Design · Official standard
Most real problems have more than one workable solution, and none of them is best on every count. In this lesson students evaluate competing solutions to complex problems, such as a city's drought water supply or a safer crossing outside a school. They first remove options that break a must-meet constraint, then compare the rest on cost, safety, reliability and aesthetics and on their social, cultural and environmental impacts. They set priorities as weights, compute weighted scores, life-cycle costs and reliability, and test how the choice changes when the priorities change. The practice is Constructing Explanations and Designing Solutions: evaluating a solution from scientific knowledge, evidence students gather, prioritized criteria and trade-offs. The core idea is ETS1.B, Developing Possible Solutions, which says that evaluating solutions means taking into account a range of constraints, including cost, safety, reliability and aesthetics, and considering social, cultural and environmental impacts.
NGSS gives no Clarification Statement and no Assessment Boundary for HS-ETS1-3, so this lesson stays with the wording of the performance expectation: every task asks students to evaluate a solution against prioritized criteria and to name the trade-offs. All costs, scores and test results on this page are invented for teaching and labeled as invented. The shoreline model lab uses sand, gravel, clay and water only, with goggles and a spill plan.
Learning Objectives
By the end of this lesson, students will be able to:
Screen competing solutions against must-meet constraints, such as a budget limit or a safety requirement, before comparing them
Compare solutions on cost (including life-cycle cost), safety, reliability and aesthetics using data
Identify social, cultural and environmental impacts of a solution and say who gains and who bears the costs
Build a weighted decision matrix from prioritized criteria and explain how the result changes when the priorities change
Write an evidence-based recommendation that names the trade-offs it accepts
Prior Knowledge Required
Students should already be comfortable with:
Evaluating competing design solutions against criteria and constraints MS-ETS1-2
Writing criteria and constraints for a design problem HS-ETS1-1
Percentages, weighted averages and simple probability
Show two photos (or quick sketches): a plain concrete flood wall and a restored marsh with a low rock edge in front of homes. Give students three minutes alone and three with a partner.
Warm-Up Prompt
"Both designs protect the same street from high water. List every reason a town might choose the wall, and every reason it might choose the marsh. Which reasons are about money, which about people, and which about nature?"
Sort the answers on the board into the seven headings of HS-ETS1-3: cost, safety, reliability, aesthetics, social, cultural and environmental. Ask which heading matters most. Students will disagree, and that is the point of the lesson: a fair evaluation makes the priorities visible instead of hiding them.
Direct Instruction20-25 minutes
The complex problem (invented data). A city of 300,000 people needs 40,000 m³ more water per day in dry years. Four options are on the table: a seawater desalination plant, a plant that purifies treated wastewater for drinking (recycling), a new reservoir in a nearby valley, and a 70 km pipeline from a neighboring river. The city can borrow at most $130 million, and every option must meet drinking-water standards.
Screen with must-meet constraints. An option that breaks a hard limit (a legal safety standard, the largest budget available) is removed or redesigned. It is not traded off against good scores elsewhere.
Choose the criteria and give each a weight. The seven considerations in the standard are the minimum list. Weights that add up to 100% make the priorities explicit, and the stakeholders should agree on them.
Gather evidence for each score. Cost over the whole life, not only the purchase price; reliability from failure or availability data; safety from hazards and standards; aesthetics from surveys of the people who will see the design; social, cultural and environmental impacts from who is affected and how.
Score and total. Score each option (here 1 = poor to 5 = excellent), multiply by the weights and add.
Test the priorities. Change the weights the way another stakeholder group would. If the winner changes, the decision depends on values, and the report must say so.
Recommend and name the trade-offs. State which option you recommend, what it gives up, and how the worst impacts could be reduced.
Decision matrix with weights A (scores 1-5, invented)
Criterion (weight)
Desalination
Recycling
Reservoir
Cost (25%)
1
3
5
Reliability (25%)
5
4
2
Safety (15%)
4
4
3
Social (10%)
3
2
3
Cultural (10%)
4
3
1
Environmental (10%)
2
4
1
Aesthetics (5%)
2
4
4
Weighted total
3.10
3.45
2.90
Screen with must-meet constraints
The pipeline costs $150 million to build; desalination costs $120 million, recycling $80 million and the reservoir $60 million. The city can borrow at most $130 million.
Result: $150 million is over $130 million, so the pipeline is out before scoring; three options remain
Life-cycle cost over 30 years
Capital cost plus 30 years of operating cost: desalination $6 million a year, recycling $4 million, reservoir $1 million.
A recycling plant with one treatment line gives full supply on 90% of dry-year days. A second identical line, able to carry the full load alone, adds $15 million of capital and $0.5 million a year to run.
Result: If the lines fail independently: 1 - 0.10 × 0.10 = 0.99, so 99% of days; 30-year cost 95 + 30 × 4.5 = $230 million
Change the priorities
Council members focused on water bills propose weights B: cost 40% and reliability 10%, the other weights unchanged.
Result: Reservoir 3.35, recycling 3.30, desalination 2.50: the top choice flips
Use Diagram 1 to show the flip and Diagram 2 to show why there is no free answer: the option with the lowest cost has the lowest reliability, and the most reliable options cost the most. Point out what the scores hide. The reservoir's cultural score of 1 comes from flooding a valley where a local community has held gatherings for generations, and its environmental score from lost stream habitat. A weighted total can let a high cost score cover up an impact that some people consider unacceptable, so the recommendation must name it in words as well.
Guided Practice15 minutes
Groups of three evaluate three ways to make a crossing safer on a two-lane street outside a school (speed limit 25 mph). The weights and scores below are invented; groups compute the totals and discuss the trade-offs.
School crossing options (scores 1-5, invented)
Criterion (weight)
Traffic signal
Raised crosswalk with flashing beacons
Pedestrian bridge
Safety (35%)
4
3
5
Cost (20%)
3
5
1
Reliability (15%)
3
4
5
Social: access for wheelchair users and strollers (10%)
4
5
2
Aesthetics (10%)
3
4
2
Cultural: fits the historic street (5%)
3
4
2
Environmental (5%)
4
5
2
Ask each group to (1) compute the three weighted totals, (2) say which option is safest and why it still does not win, and (3) decide whether the raised crosswalk would still win if its safety score dropped to 2 because some drivers ignore the beacons. Walk the room: the totals are 3.50 for the signal, 4.00 for the raised crosswalk and 3.30 for the bridge. With a safety score of 2 the crosswalk falls to 3.65, still above the signal. Groups should notice that the bridge's long ramps are what cost it the social score, and that the safety score of each option needs evidence, such as crash records at similar crossings.
Independent Practice10-15 minutes
Each student evaluates one solution they can observe: a bike lane, the school's water bottle filling stations, solar panels on a local building, or a new traffic circle. They write one line of evidence for each of the seven considerations, give each consideration a weight, and state one trade-off the solution made. Collect the pages; they are the starting point for Homework Problem 6.
Closure10 minutes
Exit Ticket
"Recycling ranked first with weights A and the reservoir ranked first with weights B. Write two sentences to the city council: what should they decide first before choosing, and what impact must they discuss no matter which weights they use?"
Look for two ideas: the council has to agree on its priorities (how much cost matters compared with reliability), and the reservoir's cultural and environmental impacts must be discussed in words, not only as scores.
Differentiation Strategies
For Struggling Students
Give a partly filled decision matrix with the weights as decimals (0.25, 0.10) and one column already worked
Provide a sorting mat with the seven headings so students can place evidence cards before scoring
Use sentence frames for the recommendation: "We recommend ___ because ___. It gives up ___. To reduce that impact, ___."
For Advanced Students
Ask students to find the smallest cost weight at which the reservoir overtakes recycling, adjusting only the cost and reliability weights
Have students argue whether cultural impacts should be a weighted score at all or a must-meet constraint decided with the affected community
Ask students to build the matrix in a spreadsheet so the weights can be changed live during a class debate
Assessment Guidance
What to Look For
Strong evaluations remove options that break a must-meet constraint before scoring, use life-cycle cost rather than purchase price, back each score with evidence, and cover all seven considerations. The weights are stated and justified, the student tests at least one other set of priorities, and the recommendation names the trade-offs it accepts and who bears them. Watch for scores with no evidence, weights chosen after the fact to favor a preferred option, and impacts on people or places that disappear into a single number.
02
Classroom Activities
3 Activities
1
Lantern Test Data: Cost, Reliability and Who Can Pay
20 minPairs
A program wants to replace kerosene lamps in homes without electricity with solar lanterns. Pairs analyze invented field-test data for three lantern models and recommend one, naming the trade-off.
The Data (invented)
Lantern 1: price $18; hours of light on a full charge over 5 test nights 5.5, 6.0, 5.0, 5.5, 6.0; 24 of 200 units failed in the first year; needs 2 battery replacements at $6 in 3 years; no phone charging; sealed lead-acid battery; user panel look rating 3.1 of 5
Lantern 2: price $25; hours 8.0, 7.5, 8.5, 8.0, 8.0; 6 of 200 failed; no battery replacement in 3 years; phone charging; lithium iron phosphate battery; look rating 3.8
Lantern 3: price $32; hours 7.0, 6.5, 7.5, 7.0, 7.0; 10 of 200 failed; 1 battery replacement at $8 in 3 years; phone charging; nickel-metal hydride battery; look rating 4.5
Procedure
Compute each lantern's mean hours of light, first-year failure rate and 3-year cost (price plus replacements)
Decide which of the seven considerations each data line belongs to. Where is the evidence for safety, social and environmental impacts?
Set weights with your partner, score each lantern 1-5 and compute the totals
Write a two-sentence recommendation that names what your choice gives up
Discussion Questions
Lantern 1 has the lowest price, but Lantern 2 has the lowest 3-year cost ($25 against $30 and $40). Why might many families still buy Lantern 1, and what could the program do about it?
Lantern 2 leads on hours of light and on reliability. Is it still a trade-off, or does one option simply win?
Lead is toxic. How should the lead-acid battery count: as an environmental score, a safety score or a reason to screen Lantern 1 out?
Modification for Distance Learning
Share the data as a spreadsheet. Each pair sets its own weights in one row, and the class compares how many pairs chose each lantern and why.
2
Shoreline Model Lab: Wall, Rock Slope or Living Shoreline
35 minGroups of 4
Coastal erosion threatens homes and roads in many places. Groups build three small shoreline protections in a tub of sand and water, make waves, and evaluate the designs on erosion, cost, aesthetics and habitat. The model shows trends, not real-world sizes.
Safety
Wear safety goggles while making waves: sandy water can splash into eyes
Keep tubs on low tables or the floor, away from outlets, laptops and phones
Wipe spills at once so nobody slips, and keep towels at every station
Put used sand in the trash bag, never down the sink, and wash hands at the end
Procedure
Build a sand beach at one end of the tub and add water to 3 cm deep. Mark the top of the beach with a ruler line
Build one design at a time in front of the beach, using the price list: modeling clay 2 credits per stick, gravel 1 credit per cup, sponge strip 1 credit each. Wall: 3 sticks of clay (6 credits). Rock slope: 5 cups of gravel over 1 stick of clay (7 credits). Living shoreline: 4 sponge strips as marsh behind 2 cups of gravel (6 credits)
Make 20 waves with the paddle at the far end, one per second, and measure how far the top of the beach moved back
Rebuild the beach before testing the next design. After all three, the class votes on which design looks best
Sample Class Data (invented)
Beach retreat after 20 waves: wall 1.5 cm, with a 1.0 cm deep scour hole at its base; rock slope 0.5 cm; living shoreline 1.0 cm. Class vote on looks (24 students): wall 3, rock slope 6, living shoreline 15. Only the living shoreline leaves places for plants and animals to live.
Discussion Questions
The rock slope eroded least but got only 6 of 24 votes on looks. How would you weight erosion against aesthetics for a public beach?
The wall lost the most sand and dug a hole at its own base. What does that suggest about its reliability over many storms?
What can this tub model not tell you about cost, cultural or social impacts on a real coast?
Challenge Variation
Give groups 8 credits to design a hybrid (for example gravel in front of sponge marsh). Before testing, they predict its retreat and its vote share, then compare.
3
Town Hall: Evaluating a Wind Farm on a Ridge
25 min5 stakeholder teams
A county is evaluating a proposal for 20 wind turbines of 3 MW each on a ridge above town. Five teams each speak for one stakeholder, then the whole class revises the weights and looks for a version of the project that reduces the worst impacts.
The 5 Stakeholder Teams
Regional utility: needs reliable, low-cost power and must cut its emissions
A local Indigenous nation: the north end of the ridge is a place of cultural significance where ceremonies are held
Bird conservation group: hawks and eagles migrate along the ridge each fall
Nearby residents: concerned about the view and noise; some landowners would receive lease payments
County budget office: the project would bring tax revenue for schools and roads
Data for All Teams (invented)
Each turbine is rated 3 MW and runs at an average of 35% of its rating over a year (8,760 hours). Assume one home uses 10,000 kWh a year. Four of the 20 turbine sites are on the north end of the ridge.
Procedure
Each team computes the yearly energy of the full project and how many homes it could supply
Each team presents its top two considerations and the weights it would use
The class evaluates a revised plan with the 4 north-end turbines removed and the turbines paused during the peak fall migration weeks, and states what it costs in energy
Discussion Questions
The full project produces about 184,000 MWh a year, enough for about 18,400 homes. How many homes does the plan without the north-end sites supply, and is the loss worth it?
Is the cultural site a score to weigh or a constraint to respect? Who should decide?
Which impact did your team leave out when it first set its weights?
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: How Priorities Change the Winner
Weighted totals for the three remaining water supply options, drawn to scale (110 pixels per point). With weights A, recycling ranks first. With weights B, which put more weight on cost and less on reliability, the reservoir edges ahead of recycling, 3.35 to 3.30. The evaluation did not change; the priorities did.
Diagram 2: The Cost and Reliability Trade-off
Invented 30-year life-cycle cost and the share of dry-year days with full supply for each option, drawn to scale. No option is both cheapest and most reliable. The dashed segment shows the second treatment line: 9 more points of reliability for $30 million more over 30 years.
04
Homework Assignment
~30 min
HS-ETS1-3 Homework: Evaluating Solutions and Trade-offs
Directions: Show every calculation with units. Back each judgment with evidence from the data, and name the trade-offs in your answers. All data are invented for practice.
Part 1: Weighing the Evidence (Problems 1-3)
An island village of 400 people wants electricity for homes and a clinic. The village council chose these weights: cost 25%, reliability 25%, environmental 20%, safety 10%, social 10%, cultural 5%, aesthetics 5%. Invented scores (1-5) in that order: diesel generator 3, 4, 1, 3, 3, 3, 2; solar panels with batteries 3, 3, 5, 4, 4, 4, 3; small wind turbines with batteries 2, 3, 4, 4, 3, 2, 2. (a) Compute the three weighted totals. (b) Rank the options. (c) Name one trade-off the top option makes.
A village well can get a hand pump or a solar-powered pump (invented data). Hand pump: $1,200 to install; breaks down on average 2 times a year; each repair costs $80 and leaves the village without the pump for 5 days. Solar pump: $6,000 to install; breaks down on average 0.5 times a year; each repair costs $400 and takes 10 days. (a) Compute each pump's 10-year cost. (b) Compute the expected number of days without the pump over 10 years for each. (c) The solar pump fills a tank that feeds taps near homes, so people no longer carry water from the well. Which consideration is that, and how would it change your evaluation?
A hospital's backup power must start when the grid fails. Each backup generator starts successfully 95% of the time (invented), and one generator can carry the whole load. The hospital's safety requirement is that backup power starts at least 99.9% of the time. (a) What is the probability that at least one of two independent generators starts? (b) How many generators are needed to meet the requirement? (c) Why is this treated as a must-meet constraint rather than one weighted score among many?
Part 2: Priorities and Impacts (Problems 4-6)
Return to the island village in Problem 1. A fuel supplier who sits on the council proposes new weights: cost 40%, reliability 35%, safety 10%, environmental 5%, social 5%, cultural 5%, aesthetics 0%. (a) Recompute the three totals with the same scores. (b) Does the ranking change? By how much does the top option lead? (c) Write two sentences to the council about what this sensitivity check shows.
A state plans a highway bypass around a small town to take trucks off its main street. The bypass would cross farmland and a wetland, pass close to a cemetery the town has used for 150 years, and take traffic away from shops on the main street. List at least one social, one cultural and one environmental impact, say who gains and who bears the cost for each, and propose one change to the design that would reduce the impact you consider most serious.
Choose the solution from your Independent Practice page (or another approved by your teacher). Write a one-page evaluation: state the problem it solves and any must-meet constraints, give evidence for all seven considerations (cost, safety, reliability, aesthetics, social, cultural and environmental impacts), set and justify weights, compute a weighted score for the solution and for at least one alternative, test one other set of weights, and end with a recommendation that names its trade-offs.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
No Credit (0 pts)
Evidence for Each Consideration
All seven considerations addressed with data or specific evidence
Most addressed, or evidence thin for some
Scores or claims with no evidence
Calculations
Weighted totals, life-cycle costs and probabilities correct with units
Correct method with one error
Calculations missing or incorrect
Priorities and Sensitivity
Weights stated and justified; a second set of weights tested and interpreted
Weights stated but not justified or not tested
No priorities stated
Recommendation and Trade-offs
Clear recommendation that names what it gives up, who is affected and how to reduce the worst impact
Recommendation given but trade-offs vague
No recommendation
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Pick an answer for each multiple-choice question; the explanation opens right away. Questions 15-20 are short answer: work them on paper before you open the sample answer. Reset quiz starts over. All data in the questions are invented for practice.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
In HS-ETS1-3, what does it mean to evaluate a solution based on prioritized criteria?
Answer: B
Prioritizing means deciding in advance how much each criterion counts, for example with weights that add up to 100%. Choice A ignores priorities altogether, choice C reduces the evaluation to one criterion, and choice D reverses the process by choosing before evaluating.
Question 2 of 20 · Multiple Choice
A city transit agency compares full-size buses over 12 years. A diesel bus costs $500,000 to buy and $60,000 a year to fuel and maintain. An electric bus costs $800,000 to buy and $25,000 a year. Which is cheaper over 12 years, and by how much?
Answer: D
Diesel: 500,000 + 12 × 60,000 = $1,220,000. Electric: 800,000 + 12 × 25,000 = $1,100,000. The electric bus is cheaper by $120,000. Choice A compares only the purchase prices, and choice B counts only the operating savings (12 × 35,000) and forgets the higher price.
Question 3 of 20 · Multiple Choice
A flood-warning system has two independent water-level sensors, and either one alone can set off the alarm. Each sensor works 80% of the time when it is needed. What is the probability that at least one works?
Answer: A
Both fail with probability 0.2 × 0.2 = 0.04, so at least one works with probability 1 - 0.04 = 0.96. Choice B is the chance that both work (0.8 × 0.8), choice C assumes the second sensor adds nothing, and choice D is 1 - 0.64, the chance that at least one fails.
Question 4 of 20 · Multiple Choice
The cheapest design for a village water heater leaves a bare electric heating element in contact with the water that people touch. How should the evaluation handle this?
Answer: C
A serious risk to people is a must-meet safety constraint, so it is fixed or the option is removed; it is not balanced against a low price. Choice A trades safety for cost, choice B puts the burden on users, and choice D files the hazard under the wrong consideration.
Question 5 of 20 · Multiple Choice
Which consideration is about aesthetics?
Answer: B
Aesthetics concerns how a design looks, sounds or feels to the people around it, so the residents' view of the tower is the aesthetic consideration. Choices A and D are reliability, and choice C is cost.
Question 6 of 20 · Multiple Choice
A city plans to replace a fixed bus route with an on-demand shuttle booked through a phone app. Which is a social impact?
Answer: A
A social impact is an effect on people and communities, including who gains access and who loses it. Choice B is an environmental impact, choice C is cost and choice D is reliability.
Question 7 of 20 · Multiple Choice
A proposed dam would supply water and power. Which of these is a cultural impact?
Answer: D
Cultural impacts concern a community's traditions, heritage and places of meaning, so losing a fishing tradition handed down through generations is cultural. Choice A is an economic and social effect, choice B is environmental and choice C is reliability.
Question 8 of 20 · Multiple Choice
Which is an environmental impact of a seawater desalination plant?
Answer: C
Brine discharge changes the water near the outlet and can harm marine life, which is an environmental impact. Choice A is a cost and social effect, choice B is aesthetics and choice D concerns operation and reliability.
Question 9 of 20 · Multiple Choice
A decision matrix weights cost 50%, reliability 30% and aesthetics 20%. An option scores 4 on cost, 2 on reliability and 5 on aesthetics. What is its weighted total?
Answer: B
0.5 × 4 + 0.3 × 2 + 0.2 × 5 = 2.0 + 0.6 + 1.0 = 3.6. Choice A is the plain average (11 ÷ 3), which ignores the priorities. Choice C is the unweighted sum, and choice D swaps the cost and aesthetics scores (0.5 × 5 + 0.3 × 2 + 0.2 × 4).
Question 10 of 20 · Multiple Choice
Option X has the highest weighted score, but it does not meet the building code for earthquake safety. What should the team do?
Answer: A
Legal and safety requirements are screens: an option that fails one is not a valid choice, however well it scores elsewhere. Choice B lets a high score buy its way past a hard limit, and choice C manipulates the weights instead of fixing the design.
Question 11 of 20 · Multiple Choice
Two projects cut carbon dioxide emissions for 10 years. Project X costs $2.0 million and cuts 400 tonnes a year. Project Y costs $1.2 million and cuts 150 tonnes a year. Which gives more reduction for the money?
Answer: D
X: $2,000,000 ÷ (400 × 10) t = $500 per tonne. Y: $1,200,000 ÷ (150 × 10) t = $800 per tonne. X costs more in total but cuts each tonne for less. Choice A looks only at the price, and choice B computes Y correctly but reaches the wrong conclusion.
Question 12 of 20 · Multiple Choice
A team's matrix ranks option P first with 3.52 and option Q second with 3.48. When the environmental weight rises from 10% to 15%, Q comes first. What is the best conclusion?
Answer: C
A small change in one weight flips the ranking, so the evidence alone does not decide: the priorities do. A good evaluation reports that openly. Choice A ignores the sensitivity check, choice B throws away useful information, and choice D is the bias the matrix is meant to prevent.
Question 13 of 20 · Multiple Choice
Invented first-year field data for four water filter designs: P, 3 of 200 units failed; Q, 8 of 400; R, 2 of 50; S, 1 of 20. Which design has the lowest failure rate?
Answer: A
Failure rate = failures ÷ units: P 1.5%, Q 2.0%, R 4.0%, S 5.0%. Choice D is the trap: S had the fewest failures (1), but only 20 units were tested, so its rate is the highest. Comparing counts instead of rates misjudges reliability.
Question 14 of 20 · Multiple Choice
Why should a team evaluating a new public water tower include aesthetics at all?
Answer: B
How a structure looks affects whether a community accepts it, so aesthetics can decide whether a sound design is built. It is one consideration among several, not the largest by rule (choice A), it is judged by people rather than instruments (choice C), and it never replaces safety (choice D).
Question 15 of 20 · Short Answer
A town is evaluating a switch from its diesel ferry to an electric ferry that charges at the dock. Give one specific consideration for each of the seven categories in HS-ETS1-3: cost, safety, reliability, aesthetics, social, cultural and environmental.
Sample answer. Cost: higher purchase price but lower fuel and maintenance costs over the ferry's life. Safety: large batteries need fire protection and a crew trained to handle a battery fire. Reliability: can the ferry keep its schedule in winter, when batteries hold less charge, and what happens if the dock charger fails? Aesthetics: quieter, no exhaust smell, and a new charging tower on the historic waterfront. Social: if fares rise, some commuters may no longer afford the ferry. Cultural: the old ferry may be part of the town's identity and festivals. Environmental: no exhaust at the dock, but battery materials must be mined and recycled. Any specific, correctly placed consideration earns credit.
Question 16 of 20 · Short Answer
A town has 400 old streetlights of 150 W each. It can replace them with 60 W LED lights at $320 each. The lights run 4,000 hours a year and electricity costs $0.15 per kWh. Compare the 10-year cost of keeping the old lights (ignore their repairs) with replacing them, and name one consideration other than cost.
Old lights: 400 × 0.150 kW × 4,000 h = 240,000 kWh a year, × $0.15 = $36,000 a year, so $360,000 in 10 years. LEDs: 400 × 0.060 kW × 4,000 h = 96,000 kWh a year, × $0.15 = $14,400 a year, so $144,000 plus $128,000 to buy = $272,000. Replacing saves $88,000 over 10 years and 144,000 kWh a year. Other considerations: the color and glare of the new light (aesthetics), light at night affecting wildlife or sleep (environmental, social), or safety from brighter streets.
Question 17 of 20 · Short Answer
A town wants flood sirens that reach every home. Two independent sirens cover the same neighborhood, and each sounds 85% of the time when triggered. What is the probability that at least one sounds? If the requirement is at least 99%, how many sirens are needed?
Both fail with probability 0.15 × 0.15 = 0.0225, so at least one sounds with probability 1 - 0.0225 = 0.9775 (97.75%), which does not meet 99%. With three sirens: 1 - 0.15³ = 1 - 0.003375 = 0.996625, about 99.7%, which meets it. Three sirens are needed, assuming they fail independently (a shared power line would break that assumption).
Question 18 of 20 · Short Answer
A city proposes widening a historic market street to four lanes to reduce traffic. Describe one social impact and one cultural impact, and suggest a design change that trades some traffic relief for a smaller impact.
Sample answer. Social: market vendors and shoppers lose sidewalk space and parking, and a wider road is harder for children and older people to cross. Cultural: the market street and its buildings are part of the community's heritage and weekly traditions, and widening may demolish historic facades. Change: keep two lanes on the market street and route through traffic onto a parallel street, or widen only at the busiest junction. Traffic relief is smaller, but the market and its buildings stay.
Question 19 of 20 · Short Answer
Give two reasons why the option with the highest weighted score is not automatically the right choice.
Any two of: (1) it may break a must-meet constraint, such as a safety code or the maximum budget; (2) the result may flip under slightly different weights, so the choice really depends on stakeholder priorities; (3) a single total can hide an impact some people find unacceptable, such as the loss of a cultural site; (4) the scores may rest on weak evidence, such as a small test sample.
Question 20 of 20 · Short Answer
A school cafeteria compares reusable trays with a new dishwasher (M) and compostable disposable trays (N). Weights: cost 30%, environmental 30%, safety and hygiene 20%, social 20%. Invented scores (1-5) in that order: M 2, 5, 4, 3; N 4, 3, 4, 4. Compute both totals. Then recompute with cost 20% and environmental 40%, and explain what changed.
First weights: M = 0.3 × 2 + 0.3 × 5 + 0.2 × 4 + 0.2 × 3 = 3.5; N = 0.3 × 4 + 0.3 × 3 + 0.2 × 4 + 0.2 × 4 = 3.7, so N ranks first. New weights: M = 0.2 × 2 + 0.4 × 5 + 0.2 × 4 + 0.2 × 3 = 3.8; N = 0.2 × 4 + 0.4 × 3 + 0.2 × 4 + 0.2 × 4 = 3.6, so M ranks first. The scores did not change; putting more weight on environmental impact than on cost reversed the choice, so the school must decide which priority it holds.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-ETS1-3 mean?
HS-ETS1-3 asks high school students to evaluate a solution to a complex real-world problem by weighing prioritized criteria and trade-offs.
The standard names the constraints to consider (cost, safety, reliability and aesthetics) and the impacts to consider (social, cultural and environmental). The code reads: HS (high school), ETS1 (Engineering Design), performance expectation 3.
Do students have to use a decision matrix for HS-ETS1-3?
No, but a weighted decision matrix is a clear way to show prioritized criteria and is widely used in engineering.
What matters is that priorities are stated, each judgment has evidence, and the trade-offs are named. A written comparison that does all three also meets the standard. A matrix has one weakness students should know: a single total can hide an impact that some people find unacceptable.
What is a trade-off in engineering?
Giving up some of one thing to get more of another, because no option is best on every criterion.
In the water supply example, the reservoir is cheapest but least reliable and floods a valley; the second treatment line buys reliability with money. Students should name each trade-off in words, not only in scores.
What is the difference between social and cultural impacts?
Social impacts are effects on people's lives and well-being, such as access, jobs, health and fairness; cultural impacts are effects on traditions, heritage, beliefs and places of meaning.
A new road that splits a neighborhood has social impacts; one that crosses a historic cemetery has cultural impacts as well. Many solutions have both.
How can students evaluate aesthetics fairly?
By asking the people who will see, hear or use the design, for example with a survey or a vote, rather than relying on the team's own taste.
Aesthetics includes noise and smell as well as looks. It is judged by people, so the evidence is their responses, reported with the number of people asked.
How is reliability measured in HS-ETS1-3?
With data on how often a solution works when needed: failure rates, time between breakdowns, days out of service or the probability of working.
Students should compare rates, not raw counts, and can compute the effect of backups: two independent parts that each work 90% of the time give 1 - 0.1 × 0.1 = 99%. That calculation assumes the parts fail independently.
How is HS-ETS1-3 different from HS-ETS1-1 and HS-ETS1-2?
HS-ETS1-1 defines the problem's criteria and constraints, HS-ETS1-2 designs a solution by breaking the problem into parts, and HS-ETS1-3 evaluates solutions against prioritized criteria and trade-offs.
HS-ETS1-4 adds a computer simulation to predict a solution's effects across systems. In a long project the four often appear in that order.
What mistakes do students make when they evaluate solutions?
Scores with no evidence, and weights chosen after the fact so that a favorite option wins.
Others include comparing purchase prices instead of life-cycle costs, comparing failure counts instead of rates, letting a high score outweigh a failed safety requirement, and leaving out the cultural and social impacts altogether.
Which science course teaches HS-ETS1-3?
Any of them: NGSS expects engineering design to be taught within the science courses.
Earth science classes often evaluate water, energy or coastal solutions, biology classes conservation or health solutions, chemistry classes materials and water treatment, and physics classes energy and safety devices.
How is HS-ETS1-3 assessed?
Through tasks where students evaluate real or realistic solutions and justify a recommendation, not through definitions alone.
State science tests aligned to NGSS handle engineering performance expectations in different ways, so check your state's test documents. In class, the homework rubric scores the evidence, the calculations, the priorities and the trade-offs.
07
Related Standards
5 standards
These standards connect to HS-ETS1-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-ETS1-2Prerequisite
Evaluate competing design solutions systematically against criteria and constraints
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
