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  1. #1
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    plane

    A four-engine plane flies safely if at least 2 of its engines are working. A two-engine plane works if at least one of its engines is working. The probability of failure of an engine is  q . Find the probability that the planes fly safely.

    So is it:  P(\text{four engine flies safely}) = \binom{4}{2}p^{2}q^{2} + \binom{4}{3}p^{3}q + p^{4} and  P(\text{two engine flies safely}) =  \binom{2}{1}pq + p^2
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  2. #2
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    Quote Originally Posted by heathrowjohnny View Post
    A four-engine plane flies safely if at least 2 of its engines are working. A two-engine plane works if at least one of its engines is working. The probability of failure of an engine is  q . Find the probability that the planes fly safely.

    So is it:  P(\text{four engine flies safely}) = \binom{4}{2}p^{2}q^{2} + \binom{4}{3}p^{3}q + p^{4} and  P(\text{two engine flies safely}) =  \binom{2}{1}pq + p^2

    Yes

    RonL
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  3. #3
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    Thanks a lot. This was one where I made an educated guess (I wanted to see if I could use a Poisson for this one). But then I realized, the poission is an estimation of the binomial. So just use binomial.
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