Question P5–P6 Working backwards
Today’s problem — free all day, every step. Every day has one.
Aiden had a packet of stickers. He gave half of them to his cousin. He then used 15 stickers to decorate his folder and had 45 stickers left. How many stickers did Aiden have at first?
Answer
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You know how it ended. Undo each step, last one first.
In this one. Work backwards: join the 15 stickers used to the 45 stickers left to rebuild the half Aiden kept, then double that half to rebuild the whole.
The question gives the final amount after a sequence of changes and asks what the amount was 'at first' or 'to begin with'.
Children undo the steps in the same order they happened rather than in reverse, or forget that a percentage profit is added to the cost price, so the final price is 120% of it, not 100%.
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