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Airlines sometimes overbook flights. Suppose that for a plane with 50 seats, 55 passengers have tickets. Define the random variable X as the number of ticketed passengers who actually show up for the flight. The probability mass function of X appears in the accompanying table. (Round your answers to 4 decimal places, if needed.) X 45 46 47 48 49 50 51 52 53 54 55 P(X = x) 0.04 0.05 0.11 0.14 0.25 0.18 0.12 0.05 0.03 0.02 0.01 (a) What is the expected value of X? (b) What is the variance of X? (c) What is the standard deviation of X? (d) Determine the probability that X is within 1 standard deviation of its mean value