Question: what is the greatest common factor of the numbers 30 and 75?
Answer: The prime numbers 5 and 3 are both factors that are common to 30 and 75. The product of these factors is 3×5 = 15. Thus, the “Greatest Common Factor” of 30 and 75 is 15. To check this result, divide 15 into 30 and then into 75, and verify that in each case the result is a whole number.