The probability of there being X unusable matches in a full box of Surelite matches is given by P(X-0)-8k, P(X-1)-5k, P(X-2) P(X-3)=k, P(X> 4) = 0. Determine the constant & and the expectation and variance of X. Two full boxes of Surelite matches are chosen at random and the total number Y of unusable les is denied. Calculate (Y4), and state the values of the expectation and variance of Y.