Help on MOD needed!!!

This problem is checking for a simple understanding of modulus. I don't want to do homework for you, but I will talk you through it.

First, answer this...

If (a number)mod5 = 0, what can you say for certain about that number?

Some hints
There are some useful mod rules you can use to solve these types of problems. Here are a couple of hints.

Mod (A + B) = mod A + mod B
mod A^B = (mod A)^B
mod AB = (mod A)(mod B)

For example

33^33 mod 5 =
3^33 mod 5 =
27^11 mod 5 =
2^11 mod 5 =
2^3 * 2^8 mod 5 =
8 * 16^2 mod 5 =
3 * 1^2 mod 5 =
3

Answering the question for my own understanding
(43^43-17^17)mod5
=(43^43)mod5-(17^17)mod5
=(43mod5)^43-(17mod5)^17
=3mod5^43-2mod5^17
=(3mod5)(3mod5)^42-(2mod5)^3(2mod5)^14
=(3mod5)(3^3mod5)^14-(2^3mod5)(2mod5)^14
=(3mod5)(27mod5)^14-(8mod5)(2mod5)^14
=(3mod5)(2mod5)^14-(3mod5)(2mod5)^14
=(3*2^14)mod5-(3*2^14)mod5
=(3*2^14-3*2^14)mod5=0mod5=0

Rap