You can estimate to find out "about how many" when subtracting as well as when adding. This is also called rounding.You can estimate the differences of two-digit and three-digit numbers.Look at the examples below. 77Rounds to8031Rounds to- 3050 The estimated difference of 77 - 31 is 50. 459Rounds to500287Rounds to- 300200 The estimated difference of 495 - 287 is 200.