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Math Help - Am I doing this correct?

  1. #1
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    Am I doing this correct?

    Doing some review hoping I'm doing this correct. Thanks!
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  2. #2
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    Re: Am I doing this correct?

    Am I doing this correct?-clipboard02.jpg

    I'm not seeing any trigonometry....

    One thing to note is that

    Pr[winning at least 3 prizes] = 1 - Pr[winning 2 or less prizes]

    which is less work than you seem to have done.

    given $p=\dfrac 1 4$ we get a (10, 1/4) binomial distribution with

    $Pr[\mbox{k prizes}] = \begin{pmatrix}10 \\k\end{pmatrix} p^k (1-p)^{10-k}$

    and you can quickly find the probability of winning 2 or less prizes as

    $(3/4)^{10} + 10 (1/4) (3/4)^9+ 45 (1/4)^2 (3/4)^8\approx 0.5256$ (it's exactly $\frac{137781}{262144}$)

    and thus

    $Pr[\mbox{winning 3 or more prizes}] \approx 1 - 0.5256 = 0.4744$
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