Grade 4 - Progress in Mathematics

Least Common Denominator

Rafael’s cookie recipe called for 


1

3 
cup

of brown sugar and 
^34 
cup of white sugar.

How much sugar did Rafael use?

Add: 


1

3 


3

4 

To add 
^13 

^34 
, rename both fractionsas fractions

with the least common denominator.

The least common denominator (LCD)

is the least common multiple of the denominators.

Multiples of 3: 0, 3, 6, 9, 12 , 15, 18, 21, 24,...

Multiples of 4: 0, 4, 8, 12 , 16, 20, 24,...

So the LCD of 
^13 
and 
^34 
is 12.

Rename the fractions. Add.

 
^13 

 31 
 44 
 142 
 
 142 

 
^34 

 43 
 33 
 192 
 
 192 




1

1

3

2 
^1 
 1

1

2 
 simplest form

Rafael used 1
 1

1

2 
cups of sugar.

Write the LCD for each set of fractions.

0 1. 


1

2 
, 

2

5 
^0 2. 

3

4 
, 

1

6 
^0 3. 

2

3 
, 

3

8 
^0 4. 

1

5 
, 

1

6 

0 5. 
 130 
, 
^14 
 0 6. 
^45 
, 
^34 
 0 7. 
^13 
, 
^15 
, 
^16 
 0 8. 
^13 
, 
^14 
, 
^15 

Add or subtract. Write the answer in simplest form.

0 9. 
^12 

^27 
 10. 
^14 

^35 
 11. 
^56 

^19 
 12. 
^23 

^12 

13. 
    ^78
    
    130
    14.
    19
    0 
    ^16
    15.
    ^79
    
    ^38
    16.
    ^58
    
    ^23
    

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