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Thread: How to reverse this calculation?

  1. #1
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    How to reverse this calculation?

    Let's say the probability of X happening is 99%
    The probability that X happens every time 10 times in a row is 0,99^10, right? So approximately 90%

    so the numbers are:
    A = 0,99
    B = 10
    C = 0,9

    How do i find A, if I know B and C?
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  2. #2
    Junior Member Cervesa's Avatar
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    Re: How to reverse this calculation?

    $A^{10}=0.9$

    $A = (0.9)^{1/10} \approx 0.99$
    Thanks from topsquark and DanishGuy
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  3. #3
    Member Walagaster's Avatar
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    Re: How to reverse this calculation?

    Quote Originally Posted by DanishGuy View Post
    Let's say the probability of X happening is 99%
    The probability that X happens every time 10 times in a row is 0,99^10, right? So approximately 90%

    so the numbers are:
    A = 0,99
    B = 10
    C = 0,9

    How do i find A, if I know B and C?
    Let me rephrase your question (and notation) and see if I understand what you are asking. We have an event with probability $p$ of happening. We then do $n$ independent trials. Let $X$ be the random variable giving the number of successes in $n$ trials. Then $P(X=n) = p^n$. I think you are asking if you know $C=p^n$ and $n$, how can you find $A=p$. And the answer is $A=\sqrt[n]{p^n} = \sqrt[n]C$.
    Thanks from topsquark and DanishGuy
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