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Probability question of flipped coins

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data

    suppose you flip 20 fair coins. what is the probability of getting the sequence HTHHTTTHTHHHTHHHHTHT in exactly that order?

    What if the order doesn't matter?

    2. Relevant equations



    3. The attempt at a solution
    Ok so in general the total possible outcomes are 2^20.
    and the #ways you can get 12 H (or the multiplicity) would be 20!/(12!(20-12)!) right?
    i don't how how to account for the order, or switch it to probability
     
  2. jcsd
  3. Feb 5, 2009 #2

    Dick

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    Science Advisor
    Homework Helper

    You know everything you need to know. There are 2^20 possibilities. If you account for order, there's only one way to succeed. If you don't there are C(20,12) ways, as you said. The probability is the number of ways to succeed over the total number of possible ways.
     
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