poisson distribution

Question

assume the number of customers arriving at canondale dealerships follows a poisson distribution and averages 16.8 every 15 minutes.  what is the probability that 25 customers will arrive in the next 30 min?

Answer 1

16.8 arrivals every 15 minutes gives a mean of (2×16.8) or 33.6 arrivals every 30 minutes.

By the Poisson formula Pr(X) = e^-λλ^x ÷ x!, write Pr(X=25) = e^-33.6(33.6)²⁵ ÷ 25! which

simplifies to 0.02374333193 equivalent to 0.024.