What's an example of a theorem with multiple ways to prove it?

Question

Please give a simple example that incorporates basic math, like basic arithmetic. Please include the theorem and the multiple proofs (can just mention them, or include the entire proofs).

Answer 1

Here's one. Choose $n+1$ integers between $1$ and $2n$, inclusive. Prove that one of your choices must divide another.

One proof uses induction on $n$. Another completely different proof uses the pigeonhole principle.