Why can the gcf of 16 and 42 be less than 16?

Answer 1

Because 16 is a factor of 16, but it's not a factor of 42.

So a number that's a factor of both 16 and 42 must be less than 16.

(It can't be more than 16, because no factor of 16 can be bigger than 16.)

Answer 2

Because 16 isn't a factor of 42.