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Stickers — Mei gives some to Jun
The ratio of Mei's stickers to Jun's stickers was 7 : 3. After Mei gave some stickers to Jun, the ratio became 3 : 2. Together they had 120 stickers throughout. How many stickers did Mei give to Jun?
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The pattern behind it: Constant total
Money moves between two people, so their total never changes.
In this one. Stickers only move between the two children, so the total never changes — which means both ratios are describing the same 120, and each one can be turned into real numbers on its own.
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
Standard Liam and Noah's cards — 7 : 5 becomes 5 : 7 The ratio of Liam's trading cards to Noah's trading cards was 7 : 5. After Liam gave some of his cards to Noah, the ratio became 5…The 33 problem patterns
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.
A PDF, and a note when new solutions go up.