Estimating Products and Quotients

September 10, 2009

Rounding

You can estimate either a product or a quotient by first rounding each number to its greatest place value.

Example A Example B

8,659 x 122 588 / 29

9,000 x 100= 600 / 30=

900,000 20

Compatible Numbers

You can estimate using compatible numbers, which are close to the actual

numbers, but are easier to solve.

Example A Example B

24 x 41 362 / 48

25 x 40= 350 / 50=

1,000 7

Range

You can estimate by finding a range. When you find a range, the exact answer is between the two

estimates.

Example:

342 X 687Round both numbers to the lesser 100 Round both numbers to the greater 100

300 x 600=180,000 400 x 700= 280,000

Underestimate Overestimate

So the product 342 x 687 is between 180,000 and 280,000!

Practice with Rounding

562X 9,031=

6,238 / 76=

798/ 87=

489 x 2,970=

Practice with Compatible Numbers

562X 9,031=

6,238 / 76=

798/ 87=

489 x 2,970=

Practice with Range

562X 9,031=

6,238 / 76=

798/ 87=

489 x 2,970=