Answer:
a) Let X be the random variable representing the number of engines that fail. Since the probability of failure for each engine is independent of each other, X follows a binomial distribution with n = 4 and p = 0.0001. Therefore, the probability distribution for the number of engine failures is:
P(X = k) = (4 choose k) * (0.0001)^k * (0.9999)^(4-k), for k = 0, 1, 2, 3, 4.
b) The expected number of engine failures is given by:
E(X) = np = 4 * 0.0001 = 0.0004.