What is greatest common factor of 45 and 75?

Answer 1

These numbers are divided by 5 without remainder, so their common factor must be divided by 5 without remainder aswell. Let's start from 45 stepping over 5 and skipping any unmatching result: not 45, not 40, not 35, not 20 (since none of 45 and 70 divide these without reminder), but it's 15 (which gives us 45/15 = 3 and 70/15 = 5, here both results are round numbers, which gives us 15 as the answer).