) A book has n typos. Two proofreaders, A and B, independently read the book. A catches each typo with probability p1 and misses it with probability q1 = 1 p1, independently, and likewise for B, who has probabilities p2 of catching and q2 = 1p2 of missing each typo. Let X1 be the number of typos caught by A, X2 be the number caught by B, and X be the number caught by at least one of the two proofreaders. Find the distribution of X