How to Estimate:

By Rounding

Addition:

Round all addends to the greatest place value of the least number.

(232 + 376+ 105 goes to 200 + 400 +100)

Be careful when addends have different place values.

(232 + 57 + 3,489 goes to 230 + 60 +3,490)

Money is rounded the same way: to the nearest ten cents, dollar, ten dollars depending on what the greatest place of the smallest number is.

Subtraction:

Same as addition.

(356 – 134 goes to 400 – 100) and (356 – 78 goes to 360 – 80)

Multiplication:

With a single digit multiplier – only round the top number and leave the single digit multiplier what it is. ( 87 times 9 goes to 90 times 9; and 567 times 4 goes to 600 times 4)

With a double digit multiplier – round both the top and bottom numbers to their greatest place values ( 543 times 76 goes to 500 times 80) ( 5634 times 63 goes to 6,000 times 60)

Division:

With a single digit divisor – keep the divisor as it is and round the dividend to the nearest compatible multiple. It can be higher or lower than the dividend. Use whatever is closest. ( 86 divided by 9 goes to 90 divided by 9. 86 is 4 lower than 90 and 86 is 5 higher than 81) ( 83 divided by 9 goes to 81 divided by 9. 81 is 2 lower than 83 and 83 is 7 lower than 90.) Add any appropriate zeroes after the compatible multiple. (503 divided by 7 goes to 490 divided by 7) (5,003 dvided by 7 goes to 4,900 divided by 7)

With a double digit divisor – round the divisor to the nearest ten. Then follow the same directions for the dividend. Add appropriate zeroes to dividend if necessary. (503 divided by 71 goes to 490 divided by 70)

Front End Estimation:

Addition – circle the numbers on the left or the front end. Add them. Write down zeroes after this sum to correspond to the number of digits that follow. Then look at the back end and see how many groups of thousands, hundreds, or tens (depending on how many digits there are) that can be made and add them to the front end.

Subtraction – circle the numbers on the left or front end. Add them. Write down zeroes after this sum to correspond to the number of digits that follow. Forget the back end.

Multiplication – circle the front end. Multiply these two numbers. Add zeroes to correspond to the number of digits that follow. Forget the back end. This is only done with a single digit multiplier. For a double digit multiplier, use rounding.