Seatbelts II. Police estimate that 80% of drivers now wear their seatbelts. They set up a safety roadblock, stopping cars to check for seatbelt use.

a) How many cars do they expect to stop before finding a driver whose seatbelt is not buckled?

b) What's the probability that the first unbelted driver is in the 6th car stopped?

c) What's the probability that the first 10 drivers are all wearing their seatbelts?

d) If they stop 30 cars during the first hour, find the mean and standard deviation of the number of drivers expected to be wearing seatbelts.

e) If they stop 120 cars during this safety check, what's the probability they find at least 20 drivers not wearing their seatbelts?