At a car rental agency, 0.34 of the cars are returned on time. A sample of 13 car rentals is studied. What is the probability that more than 3 of them are returned on time?

Question

Write only a number as your answer. Round to 2 decimal places ( for example: 0.24). Do not write as a percentage.

Answer 1

prob(ontime) = .34
prob(not ontime) = (.66)

more than 3 of 13 implies
we CAN'T have 0 return + 1 return + 2 return + 3 return

so prob(more than 3 return) = 1 - (sum of the 4 cases listed)

I will do one of the 4 cases, you do the rest

prob(3 of the 13 are returned)
= C(13,3)(.34)^3 (.66)^10
= 286(.039304)(.015884)
= appr .1763
carry about 4 decimals since you want only 2 in your answer