Bala received the same amount of allowance every week. In Week 1, he spent $45 and saved the rest. In Week 2, he spent only $27 and saved the rest. As a result, his savings increased by 40% in Week 2. How much was his weekly allowance?
- $72
- $90
- $117
- $135
Need a hint?
The increase in savings is the difference between what he spent in the two weeks. This increase is 40% of the Week 1 savings.
Worked answer
- Let the weekly allowance be $A.
- Week 1 savings = A - 45.
- Week 2 savings = A - 27.
- Increase in savings = (A - 27) - (A - 45) = 18.
- This $18 is 40% of Week 1 savings.
- Week 1 savings = 18 ÷ 40 × 100 = 45.
- Allowance = 45 + 45 = 90.
The mistake this question tests
Percentage of a new total
Pupils often take 40% of the difference in spending ($18) and add it to the Week 2 spending, getting $27 + $7.20 = $34.20, or they calculate 40% of $45 and add it to $45.
How to fix it at home →More PSLE percentage questions
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See the answer →Practise PSLE percentage until the mistakes stop.
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