Question: what is the greatest common factor of the numbers 5 and 15?
Answer: Greatest Common Factor of 5 and 15. Greatest common factor (GCF) of 5 and 15 is 5. We will now calculate the prime factors of 5 and 15, than find the greatest common factor (greatest common divisor (gcd)) of the numbers by matching the biggest common factor of 5 and 15.