First for the bus ridership, the key assumptions are:

• At each stop, each passenger alights from the bus, independently, with probability 0.2 each.
• Either 0, 1 or 2 new passengers get on the bus, with probabilities 0.5, 0.4 and 0.1, respectively. Passengers at successive stops are independent.
• Assume the bus is so large that it never becomes full, so the new passengers can always get on.
• Suppose the bus is empty when it arrives at its first stop.
• Let