What is the common denominator for 81 and 24?

Answer 1

A good strategy for looking for common denominators is to check 2, 3 and/or 5 first.

Since multiples of 5 always end in either 0 or 5, you can eliminate that.

Since multiples of 2 are always even numbers, you can eliminate that from 81.

When you try 3:

81 / 3 = 27

24 / 3 = 8

There 3 is A common denominator. Other numbers may have multiple common denominators (like 30 and 90 which have 2, 3, 5, 6, 15 and 30 in common). So be sure you observe what your question is specifically asking.