A trade-off answer names what a design gains and what it gives up, backs each with stated evidence, and then gives a judgement for the situation described. Neither side alone is a full answer.
This lesson is part of SPM subjects and learning resources. It extends comparing design choices with explicit criteria.
What is the answer frame?
Use four short sentences.
- Gain. What does the design improve?
- Cost. What does it give up or add?
- Evidence. What figure or observation shows each?
- Judgement. Which matters more here, and why?
Worked example: a solar water heater
An original scenario. A hostel considers a solar water heater. The stated evidence: it costs RM1 800 to buy and install, and saves RM30 each month on electricity.
Gain. Lower electricity use each month.
Cost. A large up-front payment.
Evidence. Payback time is 1 800 ÷ 30 = 60 months, which is 5 years. After that the saving continues.
Judgement. “If the hostel expects to stay in the building for more than five years, the heater is worth buying because the saving eventually passes the cost. If the building may close sooner, the up-front cost is the stronger concern.”
Notice that the judgement depends on a stated condition and names both sides, so it is an argument, not just a preference.
A second example: two lamps
Using original figures: an LED lamp costs RM12, uses 9 W and lasts 10 000 hours. An old-style lamp costs RM3, uses 60 W and lasts 1 000 hours.
Over 10 000 hours, the LED needs one lamp, which is RM12. The old lamp needs ten, which is 10 × RM3 = RM30. Energy used by the LED is 9 W × 10 000 h = 90 000 Wh = 90 kWh. The old lamp uses 60 × 10 000 = 600 000 Wh = 600 kWh.
The trade-off is a higher price per lamp (RM12 against RM3) for lower cost and far less energy over 10 000 hours.
The mistake to avoid
The common slip is a one-sided answer: “Solar heaters are good because they save electricity.” It leaves out the up-front cost, which is exactly what a trade-off question is asking about.
Check your answer by underlining the gain and the cost. If there is only one underline, the answer is unfinished.
Check yourself
An original case: a school replaces a normal bin with three separate recycling bins. The bins cost RM450 in total and need a student helper for 10 minutes each day. Staff estimate that 20% of the waste can now be recycled instead of sent to landfill. Write a trade-off in four sentences.
Answer
A sample: “The gain is that about 20% of the waste can be recycled rather than sent to landfill. The cost is RM450 for the bins and 10 minutes of a student helper’s time each day. The 20% is a staff estimate, so it should be checked with a real count. I judge it worthwhile because the time cost is small and the bins are a one-off purchase, but the benefit depends on students actually sorting the waste.”
Check that both sides, the figures and the limit of the evidence appear, followed by a judgement.
What to study next
Practise with the original Sustainability practice set, then read reflecting on a small original classroom investigation to use these skills on your own data. Use the structured-answer self-review tool to check that each answer names gain, cost and judgement.
For a teacher to pressure-test your trade-off answers, see online one-to-one Sustainability tuition.