A fraction is a part of a whole. It is written with a number on the top and a number on the bottom. The top number is called a numerator and the bottom number is called a denominator. In order to subtract fractions with unlike denominators, you must find a common denominator.
How to Subtract Fractions With Unlike Denominators
Find the least common multiple (LCM) of the two denominators by listing the multiples of both denominators. The lowest multiple that is common in both denominators is the LCM. The LCM is your new denominator for both fractions.
Find the new numerator for each fraction by dividing the new denominator by the original denominator. Then, multiply the answer by the original numerator. This is your new numerator.
Subtract the second new numerator from the first new numerator.
Keep the new denominator the same.