The number of typing errors made by a typist has a Poisson distribution with an average of three errors per five pages. If a page contains an error, the typist must retype the whole page. What is the expected number of pages that must be typed for a document that is 100 pages long?
I am not very familiar with distributions but I will give it a try:
Rate $λ = \frac {3}{5} = 0.6$
We are looking for the probability $P (X>0) = 1-P(X=0) = 0.45119$
Then we calculate the mean, $\frac {3}{5}.100 = 60$?
I don't know how to continue.
Thank you in advance.