## Elementary Statistics: A Step-by-Step Approach with Formula Card 9th Edition

First we calculate the probability and the mean $p=8.25/1000=0.00825$ and $\lambda=np=400\times0.00825=3.3$ Use the Poisson formula $P(X;\lambda)=\frac{e^{-\lambda}\lambda^X}{X!}$ we have $P(5;3.3)=\frac{e^{-3.3}3.3^5}{5!}=0.12$