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Probability question

  1. Feb 3, 2008 #1
    Hi all,

    It's rather long time I haven't dealt with maths. Now I have this problem.
    A man can shoot right on the target with the probability of success of p = 30%. The question is how many shots does he need to shoot to be 95% (P) successful.

    My idea is :
    Let n the number of shots needed. Then P = p^n+p^(n-1)*q+p^(n-2)*q^2....+p*q(n-1)
    where q=1-p.
    Am i right and if yes, how can I shorten the result?

    Thanks for any help.
  2. jcsd
  3. Feb 3, 2008 #2
    In the expansion p^n + n*p^(n-1) +++q^n, it is the first term that tells us the probability that all of the n shots would be successful. The next term tells us of one failue and n-1 successes. But those terms are not what we are looking for. So I think that's a start on the problem.
    Last edited: Feb 3, 2008
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