Estimating Sums and Differences

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.

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 =

Homework Time Estimate the following sums or differences 10 + 7 4) 1 + 5 11 9 16 8 2) 6 1 - 4 1 5) 4 - 5 3 4 5 9 3) 7 + 1 6) 12 - 1 8 2 17 5