How are a common denominator and a common multiple alike and different?

The Common Denominator is the bottom part of a fraction which has been matched to 2 or more fractions. For example 1/2 + 1/4 is easier if you use 2/4 + 1/4 = 3/4. You can also use it for 3/5 + 1 2/3 Becomes 3/5 + 5/3 (Improper fraction) and you change that to 9/15 + 25/15 = 34/15 = 2 4/15

A common denominator and common multiple are alike because they both go on the bottom portion of the fraction and in order to get the common denominator you need to find the common multiple of numbers.

They are different because they have different purposes and the common denominator stays the same and the common multiple is supposed to change both or one number.

hope this helped