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Math Help - HELP! Probability of odds in favor of obtaining

  1. #1
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    HELP! Probability of odds in favor of obtaining

    Compute the odds in favor of obtaining?

    At least 1 head when a single coin is tossed 3 times?


    help me please i know the answer is 7:1 but how and what did they do to get that answer?
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  2. #2
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    Re: HELP! Probability of odds in favor of obtaining

    It is certain that for three tosses that there is either no heads (event X) or at least 1 head (event Y). Thus:

    P(X)+P(Y)=1

    P(Y)=1-P(X)

    Now, what it the probability of no heads (3 tails)?
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  3. #3
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    Re: HELP! Probability of odds in favor of obtaining

    so how do they get the ratio 7:1?
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  4. #4
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    Re: HELP! Probability of odds in favor of obtaining

    I'm trying to help you find how...
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    Re: HELP! Probability of odds in favor of obtaining

    okay well thats the whole questions im not really familiar with this so i really dont know what other information i need to get to you.
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    MHF Contributor MarkFL's Avatar
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    Re: HELP! Probability of odds in favor of obtaining

    What I mean is, I am asking you to compute the probability that all three tosses are tails. Once you do this, then you can complete the question.

    What is the probability that for 1 toss, the result is tails?
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  7. #7
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    Re: HELP! Probability of odds in favor of obtaining

    1/2
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  8. #8
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    Re: HELP! Probability of odds in favor of obtaining

    Correct, so for three tosses in a row to all be tails, what would this probability be?
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    Re: HELP! Probability of odds in favor of obtaining

    3/2 ?
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    MHF Contributor MarkFL's Avatar
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    Re: HELP! Probability of odds in favor of obtaining

    No, the probability of getting the first tail AND getting the second tail AND getting the third tails is:

    (1/2)(1/2)(1/2) = 1/8

    You see, there are 8 outcomes, only one of which is 3 tails:

    HHH
    HHT
    HTH
    HTT
    THH
    THT
    TTH
    TTT
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  11. #11
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    Re: HELP! Probability of odds in favor of obtaining

    okay i see that now. so how do i go about finding the ratio ?
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  12. #12
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    Re: HELP! Probability of odds in favor of obtaining

    nvm i got it
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  13. #13
    MHF Contributor MarkFL's Avatar
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    Re: HELP! Probability of odds in favor of obtaining

    Yes, you can see now, even without the formula that there are 7 outcomes with at least 1 heads and only 1 without. The formula is useful though...for example if instead of 3 tosses there are 100 and listing the 2^100 outcomes is just not practical.
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