Any arithmetic operation such as addition or subtraction involving two or more fractions is possible if the denominators of both fractions are the same. This is known as the common denominator.
One can add or subtract fractions only when they have a common denominator. (see example below)
We can obtain common denominators by multiplying both numerator (top) and denominator (bottom) by the same amount.
Addition of 2⁄5 and 1⁄2 .
First, multiply 2⁄5 by 2⁄2 to get 4⁄10 .
Now multiply the second fraction 1⁄2 by 5⁄5 to get 5⁄10 .
The new fractions have a common denominator 10.