If three squares are selected at random from chessboard, then the probability that they form the letter "L" is

We have,n(S)=64C3Let 'E' be the event of selecting 3 squares which form the letter 'L' .The number of ways of selecting squares consisting of 4 unit squares is 7 x 7 = 49.Each square with 4 unit squares form 4 L-shapes consisting of 3 unit squares. Therefore,n(E)=7×7×4=196∴ P(E)=196 64C3