Question P5–P6 Repeated identity
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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.
Answer
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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.
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.
Children treat the two descriptions as separate quantities and add them. Both describe the same quantity, so the two must be equal.
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