Question P5–P6 Working backwards
Today’s problem — free all day, every step. Every day has one.
Ivan gave half of his money to Helen. He then spent $18 and was left with $12. How much money did Ivan have at first?
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You know how it ended. Undo each step, last one first.
In this one. Undo the story backwards: the $18 he spent and the $12 he was left with go back together to rebuild the half he kept, and one half doubles to 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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