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Baye's Rules Help

  1. Nov 20, 2011 #1
    Question:
    You have 100 coins. 99 are fair and 1 is double sided. You pick a random coin and flip it 10 times and get 10 heads in a row. What is the probability that you picked the double sided coin?

    Response / help needed:
    Probablity of picking a 1 sided coin = .01
    Probability of heads 10 times in a row with an fair coin = .5^(10)
    Probability of heads 10 times in a row with an unfair coin (assuming the head is on both sides) = 1

    So, i think, according to baye's, the equation should be
    .01*1/ (.01*1+ .5^10*.99) = .912

    Is that correct?

    Also, what would you do if you do not assume heads is on both sides?
     
  2. jcsd
  3. Nov 20, 2011 #2

    D H

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    Staff Emeritus
    Science Advisor

    Looks good!

    You would calculate P(fair coin | 10 heads in a row), which would give the same denominator as you had but the numerator would be 0.99*0.510. Taking 1 minus this value will yield the same result you obtained.
     
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