# Total number of edges in the graph

Consider a directed graph with nodes {1,2,3...n} and include an edge (i,j) whenever i<j.

According to me, it should be n(n-1)/2 but the book says it's nC2(combinations).

• "whenever inC2 edges" - what was this meant to say? Oct 5 '15 at 9:41
• @TomvanderZanden: Formatting is messing things up. Let me correct. Oct 5 '15 at 9:54

Did you try working out what n choose 2 evaluates to?

• I certainly did not. Got carried away :) Oct 5 '15 at 9:58