Question 3.9 uses a binomial distribution to count the number of twinsout of 60 students. surprisingly, the question treats a set of twins asa person. i believe that it should not be. if there is a set of twins, x should be 2 not 1. similarly if there are 2 sets of twins, x should take on 4 not 2. assume that all twins goes to the same school, let x denote the number of twins out 60 students. the probability of a twin birth is approximately 1/90. find the pmf of x.