# Number Problem 11

### From Homeworkwiki

**If two numbers have a common factor, that factor will divide their sum and difference exactly.**

True. Let x and y are two numbers and m be their common factor.

If x = am and y = bm,

we get x + y = am + bm = m(a + b) which is divisible by m

Similarly, x – y = am – bm = m(a - b) which is also divisible by m.