Question

A hot line with a full free number receives an average of 4 calls per hour for any given hour.  Find the probability that it will receive exactly 5 calls

Answer 1

$P(X=x) = \frac{e^{-λ}λ^x}{x!} \\ λ=4 \\ P(X=5) = \frac{e^{-4}4^5}{5!} = 0.1563$