Studying the probability of waiting time between two orders where the number of calls in a given period of time follows a Poisson distribution, a seller got the following probability density function for the waiting time:
$$f(W) = 0.2e^{(−0.2W)}$$
where the waiting time $W$ is measured in minutes. In this case, obtain the probability of getting at least two calls in $5$ minutes.
I wonder what are the relationships between the exponential distribution and Poisson distribution in this example. I mean, what should the parameter lambda of the Poisson distribution be?
I thought, because the given time interval is $5$ (minutes) and the parameter of the exponential distribution above is $0.2$, the lambda should be $5*0.2=1$?
Is this correct?