Sometimes when you need to find a sum or difference, you do not need an exact answer. Making a reasonable estimate is good enough. You can estimate by rounding the number(s) to something easier to work with. It is always a good idea to estimate, even when you want an exact answer. You can check your exact answer by comparing it to an estimate.

What is a good estimate for 198 + 605?
(check your answer at bottom of page)

What is a good estimate for 7.9 − 1.04?
(check your answer at bottom of page)

How do these estimates help you check

the exact sum and difference?

It makes more sense in some situations to estimate more (overestimate) or less (underestimate) than the actual amount:

overestimate what you need, to be sure to have enough

underestimate what you have already or can do yourself