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Subtraction of Fractions with Different Denominators

Subtraction of fractions with different denominators requires the following steps:

Let us look at a few examples:

Example 15/62/7

LCD of 6 and 7 is 42, so

{5/6}~*~{7/7}{2/7}~*~{6/6}

=  35/42 –  12/42

=  23/42

 

Example 2: 89/10  –  62/5

LCD of 10 and 5 is 10

89/10  –  6{2/5}~*~{2/2}

=  89/10  –  64/10

=  (8 – 6) + (9/10  –  4/10)

=  25/10

=  21/2

 

Example 3: 82/5  –  23/4

LCD of 5 and 4 is 20

8{2/5}~*~{4/4}  –  2{3/4}~*~{5/5}

88/20  –  215/20

8/20 is smaller than 15/20

so we express 88/20 as 720/20  + 8/20

=  728/20

Now back to the question –  82/5  −  23/4

=  88/20  −  215/20

=   728/20  −  215/20

=  (7 – 2) + (28/20  −  15/20)

=  5 + 13/20

=  513/20

 

Learn about Subtraction of Fractions with Like Denominators