The number of customers arriving per hour at a certain automobile service facility is assumed to follow a Poisson distribution with λ = 7 .

Question

(a) Compute the probability that more than 10 customers will arrive in a 3-hour period.

(b) What is the mean number of arrivals during a 4-hour period?

Answer 1

a. Poisson distribution mean = λ = 7 per hour or λ = 21 per three hours

P(X > 10) = 1 - P(X≤ 10)

TI 84

1 - poissoncdf(21, 10) = 0.9937

or

excel

=1 - POISSON.DIST(10,21,TRUE) = 0.9937

b. mean number of arrivals in a four hour period = λ = 7 * 4 = 28

Let me know if you have any questions about this.

Dian