Free interactive math game: Estimate Sum/Diff — Round first, then add. Part of the Rounding category on MathKite.
Taken from the generator that powers this exercise. A fresh set appears every time the page is opened, and the printable worksheet holds ten of them.
Estimating a sum or difference by rounding first.
Round each number to a convenient place, then add or subtract the rounded values in your head.
312 + 489 is roughly 300 + 500 = 800.
Calculating exactly and then rounding. Estimation is meant to round first, which is why it is quick.