A school canteen sold 840 bottles of juice in week 2. This was an increase of 25% from week 1. In week 3, the number of bottles sold decreased by 40% from week 2. By what percentage did the number of bottles sold in week 3 decrease compared with week 1?
Need a hint?
Find the week 1 number first: week 2 is 125% of week 1, so divide by 1.25, not multiply. Then compare week 3 with week 1, not week 2.
Worked answer
- 840 is 125% of week 1, so week 1 = 840 ÷ 1.25 = 672 bottles.
- Week 3 is 60% of week 2, so week 3 = 840 × 60% = 504 bottles.
- Decrease from week 1 to week 3 = 672 − 504 = 168 bottles.
- Percentage decrease = 168672 × 100% = 25%.
The mistake this question tests
Percentage of a new total
Pupils take 25% of 840 or 40% of 840 as the answer, or divide the change by the week 2 figure (840) to get 20%. The percentage change must be based on the original amount, week 1.
How to fix it at home →Wrong answers children often give:
- 20% Percentage of a new total
- 15% Percentage of a new total
More PSLE percentage questions
A shop sold 60% of its pens on Monday and 25% of the rest on Tuesday
See the answer →Structured · 4mDuring a clearance sale, a shop offered a storewide discount of 25% on all items
See the answer →Short answer · 2mThe usual price of a desk fan was $75
See the answer →MCQ · 2mA jacket sold for $24 after a discount of 20%
See the answer →Structured · 3mA survey of 600 pupils was done on their favourite fruit
See the answer →MCQ · 2mBala received the same amount of allowance every week
See the answer →Practise PSLE percentage until the mistakes stop.
Three PSLE questions, free, no sign-up. You’ll see exactly where the marks went. Then 7 days of everything for S$4.99.