Estimating Sums and Differences Lesson 4-1

Benchmark Numbers A benchmark is a number that is easy to use when you estimate. When estimating the sums and differences of fractions, we use the benchmarks 0, ½, and 1. (chart on page 171 of book)

½ ½ 3 5 + 11 25 + = Change each fraction to 0, ½, or 1. Add or subtract. 3 5 + 11 25 ½ ½ + =

Example 2 7 4 + 9 15 ½ ½ = 1 +

Estimating Mixed Numbers If you have mixed numbers, then round the fraction part up to 1 or down to 0. If the fraction is greater than ½, then round up to 1. If it is less than ½, then round down to 0.

Example 15 3 10 1 4 8 10 6 16 =

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