Question

5.9. (Computer project) Twenty computers are connected in a network. One computer be-
comes infected with a virus. Every day, this virus spreads from any infected computer to

any uninfected computer with probability 0.1. Also, every day, a computer technician takes
5 infected computers at random (or all infected computers, if their number is less than 5)
and removes the virus from them. Estimate:
(a) the expected time it takes to remove the virus from the whole network;
(b) the probability that each computer gets infected at least once;
(c) the expected number of computers that get infected.

Answer 1