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This is simple for you, hard for me

  1. Feb 23, 2004 #1
    This is simple for you, hard for me....

    I really need to know how to do a question like this for a course I am taking. Can you help????

    Out of 2 million hay fever sufferers in Canada, 82% are allergic to ragweed. If a random sample of 7 hay fever sufferers is selected,

    a) what is the probability that 3 are allergic to ragweed?

    b) What is the probability that 1 is allergic to ragweed?

    What is the formula???
  2. jcsd
  3. Feb 24, 2004 #2


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    The basic idea is to use the binomial distribution with p=.82 and q=.18.
    That is expand (p+q)n into powers of p (and q).
    Then the probability of exactly k yesses is {n,k}pkqn-k.
    I am using {n,k} to represent n!/k!(n-k)!. In your problem, n=7 and k=1 or k=3.
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