How to estimate fractions

This lesson will show how to estimate fractions when the operation is addition or subtraction.

An estimate is important when we do not need an exact answer, but we want the estimate to be as close as possible to the real answer.

The first thing you always need to do before estimating fractions is to round each fraction either to the nearest 0, 1/2, or 1.

Example #1

Estimate 3/7 + 5/9

Notice that 3/7 is close to 1/2 and 5/9 is also close to 1/2.

Therefore, an estimate for 3/7 + 5/9 is 1/2 + 1/2 = 1

Example #2

Estimate 1/12 + 3/5

Notice that 1/12 is close to 0 and 3/5 is close to 1/2.

Therefore, an estimate for 1/12 + 3/5 is 0 + 1/2 = 1/2

Example #3

Estimate 9/10 + 19/20

Notice that 9/10 is close to 1 and 19/20 is close to 1

Therefore, an estimate for 9/10 + 19/20 is 1 + 1 = 2

Example #4

Estimate 1/25 + 1/13

Notice that 1/25 is close to 0 and 1/13 is close to 0.

Therefore, an estimate for 1/25 + 1/13 is 0 + 0 = 0

Subtraction

Example #5

Estimate 12/13 - 6/11

12/13 is close to 1 and 6/11 is close to 1/2.

Therefore, an estimate for 12/13 - 6/11 is 1 - 1/2 = 1/2

Example #6

Estimate 19/20 - 29/30

19/20 is close to 1 and 29/30 is close to 1.

Therefore, an estimate for 19/20 - 29/30 is 1 - 1 =  0