Question

Let Sn;k;i be the graph whose vertex set V is the set of k-element subsets of f{1; 2;


; n}
and whose edge set E is the set of 2-element sets {A; B} with A ,B E V such that (A\B) = i.
Find the number of edges in Sn;k;i and Find the value of r such that Sn;k;i
is r-regular.
(b) Let Kn be the complete graph with vertex set V = {1; 2;


; n} whose edge set E is
the set of all 2-element sets {a; b} with a; b 2 V . Find the number of subgraphs of Kn and
nd the number of paths from 1 to n in Kn.

Answer 1

anyone has done combinatorics before ?