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Math Help - Probability problem set

  1. #1
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    Probability problem set

    I'm having alot of trouble with these homework problems and how to solve them.

    Bob sets two alarm clocks (battery−powered) to be sure he arises for his Monday 8:00 A.M. accounting exam. There is a 73 percent chance that either clock will wake Bob. What is the probability that Bob will oversleep? If Bob had three clocks, would he have a 99 percent chance of waking up?

    Half of a set of the parts are manufactured by machine A and half by machine B. Two percent of all the parts are defective. Four percent of the parts manufactured on machine A are defective. Find the probability that a part was manufactured on machine A, given that the part is defective.



    I really appreciate if anyone could help me with these

    Last edited by CaptainBlack; October 2nd 2010 at 09:58 PM. Reason: too many questions in one post
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  2. #2
    MHF Contributor harish21's Avatar
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    I'll give you a couple of hints:

    Question 1:

    I am assuming both locks A and B have the probability of 73% each of waking bob up, that is, p = 0.73
    for clock A and p=0.73 for clock B. so the probability of clock A not waking Bob up would be (1-0.73 = 0.27).Same for clock B..
    Can you now find the probability that both clocks wont wake bob up?

    Question 2:
    Probability that A is defective:  P(A) = 0.5

    Probability that the parts are defective: P(D) = 0.02

    Probability that part is defective given it was manufactured on A:  P(D|A) = 0.04

    you have to find the probability that the part was manufactured on A given that it is defective, that is, : P(A|D)

    Find P(A|D) using CONDITIONAL PROBABILITY
    Last edited by mr fantastic; October 3rd 2010 at 01:50 AM.
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