What are the common multiples of 21?

Answer 1

The common factors are 1 and 7. (7 = 1 x 7 and 21 = 3 x 7)

The only common prime factor is 7, which is also the largest common factor.

Answer 2

Multiples of 21 include 21, 42, 63, 84 and so on. For them to be common, they need to be compared to another set of multiples.

Answer 3

You need at least two numbers to find a GCF.

Answer 4

Multiples of 21 include 21, 42, 63, 84 and 105. For them to be common, they need to be compared to another set of multiples.