Let X be a random variable defined as the sum of 5 independent Bernoulli trials in which the probability of each Bernoulli taking the value 1 is given by r. Suppose that prior to the 5 Bernoulli trials, r is chosen to take one of three possible values with the following probabilities:

R=r P(R=r)

0.1 0.2

0.5 0.5

0.4 0.3

(a) Compute the joint probability distribution of X and R Are Y and R independent? Provide your reasoning.

(b) Compute the marginal distribution function of X and the unconditional mean and variance of Y

this was a question in one of the textbooks but i dont understand what X is suppose to be???