# math prob

posted by
**hsuan** on
.

It is known that the number of people who enter a bank during a time interval of

t minutes is a Poisson random variable with the parameter t. The bank opens at 8am and you

arrive at the bank at uniformly random time between 8am and 9am. Let X be the number of

people who entered the bank before you. Find the expectation and the variance of X.