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The probability that one 3 foot section of wire is defective is 0.002.

  1. Oct 23, 2011 #1
    The probability that one 3 foot section of wire is defective is 0.002. If someone has 450 feet of wire then what is the probability they will have 3 or more 3 feet sections that are defective?
     
  2. jcsd
  3. Oct 23, 2011 #2

    LCKurtz

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    Re: Probability

    What have you tried?
     
  4. Oct 23, 2011 #3

    cmb

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    Re: Probability

    I'm getting the feeling that there isn't enough information here. I think the term "probability that one 3 foot section of wire is defective is 0.002" could be interpreted in a number of ways.
     
  5. Oct 23, 2011 #4

    LCKurtz

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    Re: Probability

    I agree it is pretty ambiguous. But one could assume we are talking about dividing the wire into 150 separate 3 foot sections and interpret it that way just to have something to talk about.
     
  6. Oct 23, 2011 #5
    Re: Probability

    That is exactly what I think. At first I thought that X~Pois(λ) and that P(X=1)=0.002. But finding λ seems impossible and even the values you find do not make any sense.
     
  7. Oct 23, 2011 #6
    Re: Probability

    Perhaps X~Bin(150, 0.002).
     
  8. Oct 23, 2011 #7

    LCKurtz

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    Re: Probability


    That's what I would try (making an independence assumption).
     
  9. Oct 24, 2011 #8

    Ray Vickson

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    Re: Probability

    Well, you have a large N, small p version of the binomial, with m = N*p "moderate", so I think a Poisson approximation should be very good, indeed.

    RGV
     
  10. Oct 25, 2011 #9
    Re: Probability

    Thank you.
     
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