Answer:
0.14455
Step-by-step explanation:
Since there are 30 faulty phones out of 400. It means that the Number of working phones are; 400 - 30 = 370
Probability that you will get a working phone = 370/400 = 37/40
Probability that your roommate will get a working phone after you have gotten = 369/399
Thus,probability that both of you will get a working phone = (37/40) × (369/399) = 0.85545
Finally, probability that at least one of the two phones is faulty = 1 - 0.85545 = 0.14455