Compare Fractions

Before we compare fractions, we try to get them to have the same denominators.

We do this by using lowest common multiples.

 

Suppose we wish to compare:

7	and	4
9		6

 

We look for the smallest number that 9 and 6 go into.

This will be 18, so we change both fractions into 18ths.

 

We multiply top and bottom of 7 ninths by 2:

7	=	14
9		18

 

We multiply top and bottom of 4 sixths by 3:

4	=	12
6		18

 

So we now have

14	and	12
18		18

 

Clearly

14	>	12
18		18

 

So

7	>	4
9		6

 

 

Example

Which is bigger?

12	or	11
8		6

 

Answer

The lowest common multiple of 8 and 6 is 24, because 3 × 8 = 24 and 4 × 6 = 24.

We multiply top and bottom of 12 eighths by 3:

12	=	36
8		24

 

We multiply top and bottom of 11 sixths by 4:

11	=	44
6		24

 

Clearly

44	>	36
24		24

 

So

11	is bigger
6