An undirected graph has 8 vertices labelled 1, 2, …,8 and 31 edges. Vertices 1, 3, 5, 7 have degree 8 and vertices 2, 4, 6, 8 have degree 7. What is the degree of vertex 8?

Correct Answer: 8
Vertices 1, 3, 5, 7 have degree 8 and vertices 2, 4, 6, 8 have degree 7. By definition, sum of degree= 2 * No of edges Let x = degree of vertex 8 8 + 7 + 8 + 7 + 8 + 7 + 8 + x = 2 * 31 53 + x = 61 x = 8 Hence, degree of vertex 8 is 8.