What prime factor do 75 and 90 have in common?
The prime factors of 70 are 2, 5, and 7.
The prime factors of 90 are 2, 3, 3, and 5.
The prime factors that 70 and 90 have in common are 2 and 5.
The greatest common factor of 70 and 90 is the product of the
prime factors they have in common, so it is 2 x 5 = 10.