There is a plane with seats, and passengers have tickets. Define as the number of ticketed passengers who actually show up for the flight. Here is the pmf:

(a) what is probability that flight will accommodate all ticketed passengers who show up?

So this is ?

(b) what is the probability that not all ticketed passengers who show up can be accommodated?

so this is ?

(c) If you are first person on a standby list (which means you will be the first one to get on the plane if there are any seats available after all ticketed passengers have been accommodated), what is the probability that you will be able to take the flight? if you are the third person on the standby list?

so all seats cant be filled?