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Math Help - Biased coin

  1. #1
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    Biased coin

    Ben spins a biased coin twice. The probability that it will come down heads both times is 0.36

    What is the probability that it will come down tails both time?


    Is it 1 - 0.36 = 0.64
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  2. #2
    MHF Contributor alexmahone's Avatar
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    Quote Originally Posted by Natasha1 View Post
    What is the probability that it will come down tails both time?


    Is it 1 - 0.36 = 0.64
    No.

    (p_H)^2=0.36

    p_H=0.6

    p_T=1-p_H=1-0.6=0.4

    Probability that it will come down tails both time is (p_T)^2=0.16
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  3. #3
    Super Member Quacky's Avatar
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    Quote Originally Posted by Natasha1 View Post
    Ben spins a biased coin twice. The probability that it will come down heads both times is 0.36

    What is the probability that it will come down tails both time?


    Is it 1 - 0.36 = 0.64
    It isn't a very significant addition to what Alex said, but the reason your method is incorrect is that you haven't considered the two possible scenarios whereby you could obtain exactly one head and one tail.
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by Natasha1 View Post
    Ben spins a biased coin twice. The probability that it will come down heads both times is 0.36

    What is the probability that it will come down tails both time?


    Is it 1 - 0.36 = 0.64
    Let $$p be the probability that the coin comes down heads on a single flip. Then the probability that it comes down heads on two consecutive flips is:

    p^2=0.36

    The probability that it comes down tails on two consecutive flips is: (1-p)^2.....

    and the rest is algebra

    CB
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