Knowing how to approximate or estimate not only saves you time but can also help you check your answer to see whether it is reasonable.

#### Estimating sums

Use rounded numbers to estimate sums.

##### Example 1

Give an estimate for the sum 3,741 + 5,021 rounded to the nearest thousand.

*Note:* The symbol ≈ means *is approximately equal to*.

#### Estimating differences

Use rounded numbers to estimate differences.

##### Example 2

Give an estimate for the difference 317,753 – 115,522 rounded to the nearest hundred thousand.

#### Estimating products

Use rounded numbers to estimate products.

##### Example 3

Estimate the product of 722 × 489 by rounding to the nearest hundred.

##### If both multipliers end in 50 or are halfway numbers, then rounding one number up and one number down will give you a better estimate of the product.

##### Example 4

Estimate the product of 650 × 350 by rounding to the nearest hundred.

You can also round the first number down and the second number up and get this estimate:

In either case, your approximation is closer than it will be if you round both numbers up, which is the standard rule.

#### Estimating quotients

Use rounded numbers to estimate quotients.

##### Example 5

Estimate the quotient of 891 ÷ 288 by rounding to the nearest hundred.