We use estimation when we need to make numbers easier to work with.When we estimate we are not looking for an exact answer.To estimate we need to know how to round numbers. For the Connecticut Mastery Test (CMT), we focus on rounding numbers to the nearest 10 and nearest 100.

The general rule for rounding is to look at the digit in the one's place (for rounding to the nearest 10) or the ten's place for rounding to the nearst 100. If that digit were 5 or higher we would round up. If that digit were 4 or lower we would round down. Estimated sums and differences are found by rounding first then solving the equation.