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Mr.
Mr. Tan and Mr. Lim had the same number of stamps in their collections. After Mr. Tan gave 15% of his stamps to Mr. Lim, Mr. Tan had 24 fewer stamps than Mr. Lim. How many stamps did the two collectors have altogether?
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The pattern behind it: Constant total
Money moves between two people, so their total never changes.
In this one. A transfer of 15% makes one equal collection 15% smaller and the other 15% larger, so the gap opens by twice the amount moved: 15% + 15% = 30% of one original collection.
How to spot it
One person gives, sells or loses an amount to the other, and nobody outside the two people gains or loses anything.
Common mistake
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.
Try one like it
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All 33 patterns, one to a page — the 19 behind Primary 5 and 6 word problems, and the skills the younger years are built on. The bar model, how to spot it in the question, and the mistake children make. A booklet you can print. Free.
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