Subtracting Fractions

By: Greg StarkEC&I 831

Subtracting Fractions

Numerator--------------------Denominator Represents the number of parts into

which the whole has been divided

Represents the number of partsof a whole we have.

• As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size

• Fractions with the same denominator are called like fractions and can be subtracted from each other

Subtracting Like Fractions

34

2

4-

To subtract like fractions, subtract the numerators from each other in order and place the difference (answer) over the original denominator

= =3 - 2

4

14

Subtracting Like FractionsAnother example:

58

18

- = =5 - 1

8

48

48

÷ 4----

÷ 4=

12

Subtracting fractions from a whole

712

5125

12126

-

In order to subtract a fraction from a whole, we need to regroup one of the wholes (or “borrow”)

Look at the denominator of the fraction that is being subtracted – in this case, 12ths

This will be what we regroup the whole into so we will have like fractions

5

Subtracting fractions from a wholeAnother example:

23133

334

-

In order to subtract a fraction from a whole, we need to regroup one of the wholes (or “borrow”)

Look at the denominator of the fraction that is being subtracted – in this case, 3rds

This will be what we regroup the whole into so we will have like fractions

3

Subtracting unlike fractions

16

712

34

-

As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size The denominators of the fractions do

not match – we must find the LCM of 4 and 6 – and make equivalent like fractions, before we subtract

=

212

912 - =

X 3----X 3

X 2----X 2

Subtracting unlike fractions

25

415

23

-

As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size The denominators of the fractions do

not match – we must find the LCM of 3 and 5 – and make equivalent like fractions, before we subtract

=

615

1015 - =

X 5----X 5

X 3----X 3

Review: to subtract fractions1. If the fractions are not like fractions, convert them to equivalent like fractions2. If you have no fraction, or too little of a fraction to subtract from, regroup one

whole into the desired number of pieces (the denominator) and add them to the numerator

3. Subtract the numerators from each other in order and place the difference over the original denominator

4. Reduce the resulting fraction to lowest terms5. Change improper fractions to mixed numbers