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

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Estimating Sums and Differences

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  1. Estimating Sums and Differences

  2. 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.

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

  4. Example 2 7 4 + 9 15 ½ ½ = 1 +

  5. 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.

  6. Example 15 3 10 1 4 8 10 6 16 =

  7. 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

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