When two sets of fractions have the same bottom number, or denominator, adding and subtracting them is easy. You just need to add or subtract the top numbers, or numerators, and leave the denominator the same.
However, when the denominators are different you can’t add or subtract the fractions until the denominator is the same. The first thing you need to do in this situation is to change one of the fractions to match the denominator of the other fraction. In the example below that denominator is 6. When you change a fractions denominator, make sure you change the numerator the same amount you change the denominator. In the example below, you multiply both the numerator and the denominator by 2.
How would you solve this?:
You can’t increase the fourths into fifths since 5 can’t be evenly divided by 4, as 6 was by 3 above. In this situation you have to increase the numerators and denominators of both fractions. To find a denominator that can be divided by both 5 and 4, simply multiply 5 by 4 and get 20.