The total mass of 5 boxes is 2015 g. One of the boxes has a mass of 415 g. What is the average mass of the other 4 boxes?
- 320 g
- 400 g
- 404 g
- 500 g
Need a hint?
First find the total mass of the other 4 boxes by taking away the mass of the one box. Then divide by 4, not 5.
Worked answer
- Total mass of 5 boxes = 2015 g
- Mass of one box = 415 g
- Total mass of other 4 boxes = 2015 − 415 = 1600 g
- Average mass of the 4 boxes = 1600 ÷ 4 = 400 g
Answer: 400 g
The mistake this question tests
Habit
Average and total
Pupils often divide the remaining total by 5 instead of 4, forgetting that one box has been removed from the group.
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See the answer →Practise PSLE whole numbers until the mistakes stop.
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