Three tables listed below show random variables and their probabilities. However, only one of these is actually a probability distribution.

a.?Which of the above tables is a probability distribution?b.?Using the correct probability distribution, find the probability that?x?is:(1)?Exactly 15.(2)?No more than 10.(3)?More than 5.c. Compute the mean, variance, and standard deviation of this distribution.

P(x) P(x) P(x) 5 0.3 0.1 0.5 10 10 0.3 0.2 10 0.3 -0.2 15 0.2 0.3 15 15 20 0.4 20 0.4 20 0.4