Question P5–P6 Constant total
Today’s problem — free all day, every step. Every day has one.
Priya and Zara had a total of 160 marbles. Priya gave of her marbles to Zara. Zara then gave of her marbles to Priya. In the end, each of them had the same number of marbles. How many marbles did each of them have at first?
Answer
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Money moves between two people, so their total never changes.
In this one. Keep the total fixed at 160, use the equal ending to get 80 each, then undo the two gifts one at a time in reverse order.
One person gives, sells or loses an amount to the other, and nobody outside the two people gains or loses anything.
Children draw different totals before and after, or forget that moving an amount from one person to the other changes the gap between them by twice that amount.
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