What is the highest common denominator of 18?

Answer 1

There is no highest common multiple. Once you get a common multiple - for example, multiplying 18 x 57, or using prime factorization to get the smallest common multiple - you can multiply it by 2, by 3, by 4, etc. and get ever-larger common multiples.

Answer 2

The highest common denominator of any set of denominators is infinite.

Answer 3

The greatest common denominator is infinite. The LCM is 36.

Answer 4

The GCF is 2.