Chapter 5 - Discrete Probability Distributions - 5-5 Poisson Probability Distributions - Basic Skills and Concepts - Page 232: 2

$\mu=\frac{535}{576}=0.929$

In the Poisson distribution $\mu$ is the average rate of occurence and then the probability of x successes occuring is: $P=\frac{\mu^k\cdot e^{-\mu}}{x!}$ in which $e\approx2.718$, and the mean and the variance of the distribution are both $\mu$. Here, $\mu=\frac{535}{576}=0.929, x=2.$