A group of people decide to use the elevator in an otherwise deserted 10-story building. Each of these people chooses th

[answerhappygod]

A group of people decide to use the elevator in an otherwise
deserted 10-story building. Each of these people chooses their
floor independently of the others, and completely at random, so
that each person selects a floor with probability 1/10. Let S equal
the number of stops of the elevator. (A) Give the probability that
the elevator stops at least once (b) What is the probability that
the elevator does not stop on the second floor knowing that it has
stopped at the second floor. first floor.