If a 5-regular graph has 100 vertices, how many edges does it have?

Question

I'm currently taking an introductory course in graph theory, and this problem is giving me a bit of a hard time. Where would I even start? Thanks a bunch?

Answer 1

Hint

$5-$regular means degree of each vertex is $5$. Number of edges is $\frac{1}{2}(\text{sum of degrees})$.

Answer 2

Imagine cutting all the edges in half. Now you have 100 vertices, each with exactly 5 half-edges. So how many whole edges does that make?