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Homework Help: 10th Grade IGCSE Mathematics HELP!

  1. May 13, 2004 #1
    I am having a problem with one of my Probability homework questions.

    A goalkeepr expects to save one penalty out of every three. Calculate the probability that he :

    1- Saves one penalty out of the next three,

    2- Fails to save any of the next three penalties,

    3- Saves two out of the next three penalties.

    Help. :smile:
     
  2. jcsd
  3. May 13, 2004 #2

    ShawnD

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    Science Advisor

    IIRC, the method was
    probability = (probability of yes)^(# of yes) * (probability of no)^(# of no)

    For 1 it would be

    [tex](\frac{1}{3})^1 * (\frac{2}{3})^2[/tex]

    = 0.148


    I could be wrong though.
     
  4. May 13, 2004 #3
    Shawn's close, but you forgot to consider the order. That is indeed the probability that he will make one save and two misses, but he could do that in 3 different ways, i.e. make the save on the first or the second or the third.

    What you're looking for is

    [tex]\binom{n}{m}p^m(1-p)^{n-m}[/tex]

    if p is the probability of success, n is the number of tries, and m is the number of successes.

    cookiemonster
     
    Last edited: May 13, 2004
  5. May 14, 2004 #4
    Thanks , that was a big help.
     
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