Question 48
MediumOriginal questionThe price of petrol rises by 20%, and a family reduces its petrol consumption by 10%. By what percentage does the family's spending on petrol rise?
Show the answer and explanation
CorrectNot quiteAnswer B
Correct answer: B
Explanation
Spending = price × consumption, so it becomes times.
Spending rises by 8%. (Formula: .)
Worth noting
Simply subtracting gives 10%; the cross term is −2 here, not +2 (which would give 12%).
- Concept
- Net effect of a price rise and a consumption cut
- Typical timeTypical
- 50 s
- Your timeYours
- —
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Ten questions from Percentages, at your own pace.