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Cookies and jellybeans — Mei and Wei trade
Mei bought some cookies and gave half of them to Wei. Wei bought some jellybeans and gave half of them to Mei. Mei ate 8 jellybeans and Wei ate 12 cookies. The ratio of Mei's jellybeans to cookies becomes 1:6 and the ratio of Wei's jellybeans to cookies becomes 1:4. How many jellybeans did Wei buy?
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The pattern behind it: Repeated identity
One length or count, described two ways in the same question.
In this one. Splitting each collection in half and swapping makes both children's pre-eating stashes identical, so their common cookie amount can be written in two ways and the expressions can be set equal.
How to spot it
A shape or count is described from two viewpoints in the same question, such as one edge measured as a number of long pieces and again as a number of short pieces.
Common mistake
Children treat the two descriptions as separate quantities and add them. Both describe the same quantity, so the two must be equal.
Try one like it
Standard Water — poured into a second container A rectangular tank measures 30 cm by 20 cm by 25 cm. It is 3/5 full of water. All the water is poured into a second rectangular co…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.
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