Adding fractions and Subtracting fractions with like denominators

Adding fractions and subtracting fractions with like denominators (bottom number) is easy, because all you have to do is add or subtract the numerators together (top number) . You only add or subtract the numerators because the denominators have the same number, which means they have the same number to make a whole. So you don't worry about adding the denominators. Lastly, if you fraction isn't in lowest terms (simplified) then make it in lowest terms. But how? Divide the fractions with it's biggest common multiple.

Example:

21/30 - 11/30 = 10/30 divided by 10 (biggest common multiple) = 1/3

Adding fractions & subtracting fractions (without lowest terms):

1/4 + 2/4 = 3/4    (1 + 2 = 3 --> then just put the denominator in the fraction.)
                                                                      ^ (3/4)
3/4 - 2/4 = 1/4    (3 - 2 = 1 --> then just put the denominator in the fraction.)
                                                                      ^ (1/4)