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Two bakers — cream buns and red bean buns
Mrs Tan and Mr Goh are bakers who each baked the same total number of buns yesterday: 120 buns, made up only of cream buns and red bean buns. Mrs Tan baked 15 more cream buns than Mr Goh. Mr Goh baked 30 cream buns. Each cream bun sells for $1.20 and each red bean bun sells for $0.80. Each cream bun weighs 80 g and each red bean bun weighs 70 g.
- (a) Whose buns are worth more in total sales value, and by how much?
- (b) What is the total weight of Mr Goh's buns, in kilograms?
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The pattern behind it: Repeated identity
One length or count, described two ways in the same question.
In this one. When two equal totals contain the same two types, match and cancel everything identical; only the 15 buns whose type was swapped can change the total value.
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
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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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