You have an important test tomorrow morning and want to be sure to wake up at 6:00 AM to study.Without an alarm to wake you up, you know you have no chance.You have an alarm clock that works 80% of the time.To be on the safe side, you decide to set your alarm clock plus your two roommates' alarm clocks-each of which is also 80% reliable.With the three clocks set, how likely is it that you will be awakened at the time you want? (Assume statistical independence.)
A).64
B).001
C).992
D).512
E).488

Question

Quizplus · Accepted Answer

The probability that all three alarms fail is (0.2)^3 = 0.008. Therefore, the probability of waking up (at least one alarm works) is 1 - 0.008 = 0.992.

You Have an Important Test Tomorrow Morning and Want to Be