If S={1,2,3,4,5} and R={(x,y):x+y<6} then n(R)=

We have x,y∈R iff x+y<6 Given the value x=1, we get possible values of y=1, 2, 3, 4.Thus 1R1, 1R2, 1R3, and 1R4.similarly we may find other values.The set of such ordered pairs are R={(1,1),(1,2)(1,3)(1,4),(2,1)(2,2),(2,3),(3,1),(3,2),(4,1)} ∴  n(R )=10