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Math Help - Gaussian Distribution

  1. #1
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    Gaussian Distribution

    The strength levels of a group of Martians follows Normal distribution with a mean of 75kgf and a std. dev. of 5kgf.

    (a) How many Martians do you expect to meet before you find one with a strength level greater than 72 kgf?

    (b) In a group of 5 Martians, what is the probability that exactly 4 Martians have strength levels greater than 72 kgf?

    (c) 4 Martians are trying to open a huge stone door which will open only if all of their individual strength levels are greater than 72 kgf. What is the probability that they will open the door?

    EDIT: Never mind I figured out (a) and (c). Still need help on (b), though. Thanks. I'll probably kick myself for not seeing it, but oh well.
    Last edited by thefirsthokage; April 17th 2007 at 03:21 PM.
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by thefirsthokage View Post
    The strength levels of a group of Martians follows Normal distribution with a mean of 75kgf and a std. dev. of 5kgf.

    (a) How many Martians do you expect to meet before you find one with a strength level greater than 72 kgf?

    (b) In a group of 5 Martians, what is the probability that exactly 4 Martians have strength levels greater than 72 kgf?

    (c) 4 Martians are trying to open a huge stone door which will open only if all of their individual strength levels are greater than 72 kgf. What is the probability that they will open the door?

    EDIT: Never mind I figured out (a) and (c). Still need help on (b), though. Thanks. I'll probably kick myself for not seeing it, but oh well.
    Calculate the probability p(72) that a martian has strength > 72 kgf. Then
    the number with strength >72 kgf in a sample of 5 has a binomial distribution
    B(p(72), 5). So prob of 4 having strength >72 kgf is b(4, p(72), 5).

    RonL
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