The number of errors found in each chapter of a book is dist

The number of errors found in each chapter of a book is distributed according to a Poisson distribution with variance of 20. If each chapter of the book has exactly 40 pages, calculate the probability that we find at most 1 error in a randomly selected page.

Solution

P(Xless than equal to 1)=P(X=0)+P(X=1)=e^-20*20^0/0!+e^-20*20^1/1!