What does estimate each sm or difference mean?

Answer 1

In arithmetic, estimate usually means rounding the numbers so they're easier to manipulate. Example: Estimate the sum of 432 and 267. You can round them to 430 and 270 and estimate the sum as 700. You could also round them to 400 and 300 and estimate the same total. To estimate a difference, just subtract them. 430 minus 270 is 160. The actual sum is 699 and the actual difference is 165, so your estimates came pretty close.