19. Consider the following probability distribution of a random variable X. (The question mark represents a missing probability, but you should be able to gure out What it is.) :10 20 30 p(m) 0.3 0.3 40 0.3 50 ? What is the standard deviation of the random variable X? (a) 9.8 (b) 10.2 (c) 12.9 (d) 14.1 (e) 15.7