Rounding is a procedure sometimes used in estimating the result of an arithmetic operation.
rounding whole numbers
Rounding a whole number usually results in a number that is close to the original number and has the same number of digits, but more of the digits are zeros.
During her stay at camp, Anna had 12 hours of horseback riding lessons. She also rode on trail rides for 17 hours. About how many hours did Anna get to ride horses while she was at camp?
12, rounded to the nearest 10, is 10.
17, rounded to the nearest 10, is 20.
10 + 20 = 30
Thus, Anna rode a horse about 30 hours while she was at camp.
rounding common fractions or mixed numbers
One way to round a common fraction or common mixed number is to round to the nearest whole number.
While fishing, Barbara caught, measured, and then released two sunfish. The larger one was 5 inches, and the smaller one was 4 inches long. About how much longer was the larger fish?
5, rounded to the nearest whole number, is 6
4, rounded to the nearest whole number, is 4
6 - 4 = 2
Thus, the larger fish was about 2 inches longer than the smaller one.
rounding decimal fractions or decimal mixed numbers
Cliff and Clara bought a large pizza for $11.25. They also bought a small pizza for $5.95. About how much did they pay for both pizzas?
$11.25, rounded to the nearest whole number (or dollar), is $11
$5.95, rounded to the nearest whole number (or dollar), is $6
11 + 6 = 17
Thus, Cliff and Clara paid about $17 for both pizzas.
See also estimation strategies.