Estimating Sums and Differences

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.

Change each fraction to 0, ½, or 1. Add or subtract. 5 3 25 11 ½ 0 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 4 16 10 10 1 8 6

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