These six Estimate Sums and Differences organizers with answer keys provide two different ways to estimate addition and subtraction problems. These estimation sheets also assist in rounding as that skill is required for both methods. Great compare and contrast discussions occur after seeing if Estimation Method #1 or Estimation Method #2 is more accurate. Usually, estimation method #2 is more accurate, but sometimes there are exceptions. The students love it when the sum or difference is the same or, on that rare occasion, when estimation method #1 is better.