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Four parcels — the mean mass
The mean mass of four parcels is 24 kg. Three of the parcels have masses of 19 kg, 26 kg, and 30 kg. Find the mass of the fourth parcel.
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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 mean is a total shared out equally — so multiply it back by the count to recover the total, then take away the parts you already know.
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.
A PDF, and a note when new solutions go up.