My probability skills are rusty and I simply wish to enquire the precise set of areas I need to brush up in order to solve the following problem:
Suppose users share a l Mbps link for packet transmission. Each user requires 100 Kbps when transmitting, but each user only has packets to transmit 10 percent of the time.
(a) What is the probability that at any given time, a particular user has something to transmit?
(b) Suppose there are 50 users. What is the probability that at any given time, n out of the 50 users have something to transmit?
(c) For 50 users, find the probability that there are 11 or more users transmitting simultaneously. [You can use an approximation such as the Normal approximation to the binomial; you can also do a more exact computation by using a recursive evaluation of binomial probabilities, starting from evaluation of P(0 of 50 users active)].
You can assume I fathom the communication technology aspect of the question but am extremely clueless on the probabity side.
Would appreciate if links to online help can be suggested.