Problem 7. Sum of a random number of rv's
2 points possible (graded)
A fair coin is flipped independently until the first Heads is observed: Let the random variable K be the number of tosses until the first Heads is observed plus 1. For example, if we see TTTHTH, then K = 5. For k = 1, 2, K, let Xk be a continuous random variable that is uniform over the interval [0, 5]. The Xk are independent of one another and of the coin flips. Let X = ∑(from k=1 to K) Xk. Find the mean and variance of X. You may use the fact that the mean and variance of a geometric random variable with parameter p are 1/p and (1-p)/p, respectively:
E[X]
Var(X)