Fractions can be added and subtracted easily if they have the same denominator.
Example: 2/7 + 3/7 = 5/7
3/7 − 2/7 = 1/7
If fractions don’t have the same denominator, they have to be changed to equivalent fractions first by finding the lowest common denominator (LCD).
[The lowest common denominator (LCD) can be obtained by finding the lowest common multiple (LCM) of the denominators.]
Photo : coolmath4kids.com