1. The problem statement, all variables and given/known data Assume that the probability of error-free transmission of a message over a communication channel is p=0.9. If a message is not transmitted correctly, a retransmission is initiated. This procedure is repeated until a correct transmission occurs. Such a channel is often called a feedback channel. Assuming that successive transmissions are independent, A- What is the probability that no retransmissions are required? (Note: Number of retransmissions = Number of transmissions - 1.) B- What is the probability that exactly two retransmissions are required? C- What is the expected number of retransmissions? D- What is the variance of the number of retransmissions? 2. Relevant equations A-.9 C-.1 3. The attempt at a solution B- (1-p)(1-p)= (.1)(.1)=.01 which was wrong D- Std(X)= sqrt( np (1-p)) = .1 and the variance is the std squared so var(X)=.01 which was also wrong What did I miss?