Answers

2016-07-21T21:22:14+08:00
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2016-07-21T21:23:24+08:00
For example, estimate the following sums:


36 + 21, 74 + 15, and 85 + 24


36 + 21 = 40 + 20 = 60


74 + 15 = 70 + 20 = 90


85 + 24 = 90 + 20 = 110
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