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Shop sales — a sixth day pulls the average down
A shop recorded sales of $420, $380, $510, $490, and $450 over five days. What is the average daily sale? On the sixth day, the average sales over all six days was $450. What were the sales on the sixth day?
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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. A new value only moves an average if it differs from it — the average was already $450 and stayed $450, so the sixth day must be $450 itself.
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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