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Tammy — three boxes of apples
Tammy has 3 boxes of apples. Box A is 550 g heavier than Box B and 770 g heavier than Box C. The average mass of the 3 boxes is 2150 g. What is the average mass of Box B and Box C?
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The pattern behind it: An average is a total
Turn the average back into a total before doing anything with it.
In this one. An average is a disguised total — 3 × 2150 = 6450 g — and once every box is written against the smallest one, the three bars level to a common length and the two given extras (220 g and 770 g) can be cut off that total.
How to spot it
The word 'average' appears alongside a group being split into two parts, or two separate journeys or trips being combined into one overall figure.
Common mistake
Children average two averages directly, such as averaging two speeds or two group averages, without weighting by how many, or how long, each part actually covers.
Try one like it
Standard A bakery's week — average daily sales A bakery recorded its sales over 5 days: $42, $48, $55, $51 and $44. What was the average daily sales amount over the 5 days?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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