Question

In a sample of 400 customers, 140 say that service is poor. You select two customers without replacement to get more information on their satisfaction. What is the probability that both say service is poor?

Answer 1

= 973 / 7890

Explanation:

P (A∩B) = P (A) * P (B║A)

P (A) = 140 / 400

= 7/20

Because it is without replacement this is a conditional probability of an event with respect to another event;

P (B║A) = 139/399

P (A∩B) = 7/20 * 139/399

= 973 / 7890