The pattern
Percentage change
Compare how much an amount changed with its original value.
A price that falls from one amount to a smaller one has two numbers in play, and only one of them is the reference point for a percentage: the original, starting price. Work out how much the price dropped by, then compare that drop with the original price, not with the new, lower one, since comparing against the wrong price gives a different, wrong percentage.
How to spot it
A quantity falls or rises from one stated figure to another, and the question asks for the percentage change. Words like 'decrease' and 'original price' give it away.
Common mistake
Children divide the drop by the new, lower price instead of the original price, which inflates the percentage they report.
2 worked solutions
Standard
- backpack — percentage decrease The price of a backpack falls from $400 to $300. Find the percentage decrease.
- jacket — percentage decrease The price of a jacket falls from $240 to $192. Find the percentage decrease.
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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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