Grade 4 - Progress in Mathematics

Subtract Fractions: Unlike Denominators

9-8

Lila had 
^1112 
ft of balsa wood. She used


^14 
ft of the wood to make a miniature chair

for her dollhouse. How much wood did

Lila have left?

To find how much she had left,

subtract: 
^1112 

^14 

To subtract fractions with unlike denominators:

• First find the LCM.


• Use the LCM to rename
  as fractions with
  like denominators.


• Then subtract the like fractions.

^1112 

^14 
^33 
^1112 

^1112 

^1112 




1

4 


1

4





3


 3 
 1

3

2 
 
 1

3

2 
 
 1

3


 2

 182 

 182 

^23 


Lila had 


2

3 
ft of wood left.

Study these examples.


^34 

^14 
 33 
^34 
 
^23 

^23 
^33 
^69 


^12 

^12 
 22 
^24 
 
^69 

^14 
^33 
^69 

^14 
 
^09 
 0

Multiples of 4: 4, 8, 12 , 16, 20,...

Multiples of 12: 12 , 24, 36,...

LCM of 4 and 12: 12

Write the difference

in simplest form.

Subtract the numerators.

Write the like

denominator.

Rename the

fractions.

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