Let p be a prime number. Let A be an integer divisible by p but B be an integer not be divisible by p. Let A/B be an integer. How do I prove that A/B is divisible by p? This sounds like a simple question but I just can't get it. I'm doing it in relation to proving Fermat's little theorem. (a^p = a mod p for all integers a) I'm trying to understand why the binomial coefficients in the binomial expansion of (1+a)^n are all divisible by p (=0 mod p) for all the terms with powers [1, p-1].