Subtraction of Unlike Fractions
Steps to Subtract Unlike Fractions
Step 1: Use LCM method to convert the unlike fractions into like fractions.
Step 2: Find out new numerators of the given fractions.
Step 3: Find difference of new numerators.
Step 4: Write the resulting numerator after subtraction over the LCM as denominator.
Step 5: If resultant fraction is an improper fraction then convert it into mixed fraction.
Example 1:
Here denominators are different. So, we will first make denominators of the given fractions equal, using LCM method.
LCM OF 3 and 4
= 3x4
= 12
Now we have to find out new numerators of the both fractions.
New Numerator of the first fraction =
LCM ÷ Denominator of the first fraction x Numerator of the first fraction
= 12 ÷ 3 = 4 (LCM ÷ Denominator of the first fraction)
= 4x2 =8 (Resultant answer x Numerator of the first fraction)
New numerator of first fraction is 8
New Numerator of the second fraction =
LCM ÷ Denominator of the second fraction x Numerator of the second fraction
= 12 ÷ 4 = 3 (LCM ÷ Denominator of the second fraction)
= 3x1 =3 (Resultant answer x Numerator of the second fraction)
New numerator of second fraction is 3
Now subtract new numerators
= 8  3
= 5
Then write the resulting numerator after subtraction over the LCM as denominator.
Example 2:
Here denominators are different. So, we will first make denominators of the given fractions equal, using LCM method.
LCM OF 7 and 14
7 
7, 14 
2 
1, 2 

1, 1 
= 7 x 2
= 14
Now we have to find out new numerators of the fractions.
New Numerator of the first fraction =
LCM ÷ Denominator of the first fraction x Numerator of the first fraction
= 14 ÷ 7 = 2 (LCM ÷ Denominator of the first fraction)
= 2x4 = 8 (Resultant answer x Numerator of the first fraction)
New numerator of first fraction is 8
New Numerator of the second fraction =
LCM ÷ Denominator of the second fraction x Numerator of the second fraction
= 14 ÷ 14 = 1 (LCM ÷ Denominator of the second fraction)
= 1x1 =1 (Resultant answer x Numerator of the second fraction)
New numerator of second fraction is 1
Now subtract the new numerators
= 8  1
= 7
Then write the resulting numerator after subtraction over the LCM as denominator.
Note:
1. In subtraction of a whole number and a fractional number, we assume denominator of whole number as 1 for calculation.
2. In subtraction of mixed fractions, convert mixed fraction into improper fraction before starting to subtract.