Question

In a store, an average of 10 customers enters per hour. What is the probability that at most 80 customers enter the store during a 10 hour day?

Answer 1

The random variable X of the number of customers during 10 hours has the
Poisson
distribution with E(X) = 100, (lambda = 100).
P(X <= 80) =
p0+p1+...+p80 = 0.0226492,
where pk = lambda^k * exp(-lambda) / k!