I will demonstrate with different numbers.
Find the greatest common factor of 24 and and 60.
First find the prime number decomposition of each of the numbers.

24 = 2^{3} x 3 and 60 = 2^{2} x 3 x 5

Thus 3 divides both 24 and 60, 2 divides both 24 and 60 and also 2^{2} divides both 24 and 60. No other primes or powers of a prime divide both 24 and 60. Thus the largest integer that divides both 24 and 60 is 3 x 2^{2} = 12.

Penny

Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.