Suppose that on a particular stretch of highway, the time between automobile accidents is a Poisson process with an average of 3 accidents per week.

A. Find the probability density function for the time T between automobile accidents.

B. Find the probability mass function for the number of accidents Y per week.

Not sure about A, but B is it...

f(y) = e^(neg lambda) * [(lambda^y)/(y!)]

What is the prob density function here?