1 how do I know if it's a yes or a no

1. Determine whether or not the following table is a valid probability distribution of a discrete random variable. Explain why or why not. a) X 0 1 2 3 P(X) -0.2 0. 1 0.6 0.5 b) X -1 2 3 10 P(X) 0.2 0.1 0.3 0.5 C) X 15 16 17 18 P(X) 0.27 0.28 0.32 0.13 (2007)