How do you add and subtract fractions?

Before you add or subtract fractions you must have a common denominator. 1/2 + 1/2 = 2/2 = 1 that was easy as there was a common denominator. 1/3 + 1/4 = before you can complete this you must have a common denominator as 3 and 4 are not common (same). We reach a common denominator of 12 by either cross multiplying (3 x 4) or look for lowest common multiple (same number in both times table), so that is 12. So we can now add 4/12 + 3/12 = 7 /12 ... Important to remember what ever did to achieve new denominator of 12 you must do the same for the numerator. For example fir the first fraction you multiplied 3 by 4 to get 12 so you must multiply the numerator 1 by 4 to get 4/12.