During normal business hours at a gas station, customers arrive, ...

[abarnes]

During normal business hours at a gas station, customers arrive, on average, every ten minutes. Assume that the distribution of the time between arrivals follows an exponential distribution. Suppose that a customer has just left the gas station.
 
  What is the probability that the cashier at the gas station has more than 15 minutes before the next customer arrive?

Question 2

The total degrees of freedom is:
 
  A) 21
  B) 22
  C) 23
  D) 24

[Perkypinki]

Answer to Question 1

Exponential with mean 1/ = 10, then,  = 0.10, and P(T > 15 ) = e-15 = e-1.5 = 0.223

Answer to Question 2

C