What is the greatest common factors of 15 and 42?

15 can be factorized into 3 x 5

42 is factorized as 2 x 3 x 7

Of these factors of these two, greatest common factor is 3.

Where as the LCM is found by multiplying the common factor along with non common ones. ie 3 X 2 X 5 X 7 = 210

So HCF or GCF or GCD (Greatest Common Divisor) is 3

Least common multiple is 210