Three musicians pick seven pieces of music out of 22 pieces independently of each other. they play one piece of music together only if the piece is chosen by all three of them. let x be the random variable which denote the number of pieces of music played. determine the expected value and the variance of x and compute p{x\geqslant1}. hint: to do this let xi to be 1 if the three musicians picks the ith music piece and 0 otherwise. express x in terms of xi. are the xi's independent?