Answer to Question #98384 in Statistics and Probability for debra gross

Question

A new website has an average random hit rate of 20.5 unique visitors every hour. what is the probability of getting exactly 30 unique visitors in any one hour?
Expert Answer

Answer 1

Let $X=$ the number of unique visitors every hour: $X\sim P(\lambda)$

$$P(X=x)={e^{-\lambda}\cdot\lambda^x \over x!}$$

Given that $\lambda=20.5$

$$P(X=30)={e^{-20.5}\cdot(20.5)^{30} \over 30!}\approx0.010615$$

The probability of getting exactly 30 unique visitors in any one hour is $0.0106$