Use the Multiplication Rule for Independent Events
-CampusFest is a student festival where local businesses come on campus to sell their goods to students at vastly reduced prices. As part of a give-away promotion, a local cellular phone company gave away 500 cellular phones to students who signed up for their calling service. Unbeknownst to the company is that 70 of these cellular phones were faulty and will cause a small explosion when dialed outside the local calling area. Suppose you and your roommate each received one of the giveaway phones. Find the probability that both of you received faulty phones.
A) 0.01936
B) 0.0196
C) 0.28
D) 0.12064

Question

Quizplus · Accepted Answer

The probability that one phone is faulty is 70/500. After one faulty phone is given away, the probability the next phone is faulty is 69/499. Multiplying these probabilities gives (70/500) * (69/499) = 0.01936.