subtract within 100
Calculate 85 − 37 within 100.
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The pattern behind it: Units and parts
Cut one amount into equal shares. One number tells you what a share is worth.
In this one. Tens come off tens and ones off ones, and a ten can be renamed as ten ones when the ones run short.
How to spot it
A single amount is split by a ratio, a fraction or a percentage. One extra number gives you the leftover, the difference, or the value of one share.
Common mistake
Children match the given number to the wrong number of shares, using the whole bar when the number covers only the leftover or the difference between two people's shares.
Try one like it
Standard add in columns Use a written addition algorithm to calculate 46 + 35.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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