Add 1 more or less than a multiple of 10
Add 1 more or less than a multiple of 10
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2.NBT.5
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About This Sprint
Use multiples of 10 as benchmarks to add 2-digit numbers with 1 or 9 in the ones place, e.g.
37 + 20 = 57
37 + 21 is one more than 57
37 + 19 is one less than 57