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Math Help - [SOLVED] simple math stats

  1. #1
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    [SOLVED] simple math stats

    Hi, so i have to find the probability in a random sample to find that the average lies between 475 and 540 with mean 500 and st.dev 125. the z-values i got for 475 is -1 and for 540 1.6. I look on the z-table to find that the p-value for -1 is 0.1587 and 1.6 0.05487.

    The sum of those two is 0.2135 and that would be the probability right? but the answer sheet says its 0.7865. what did i do wrong? greatly appreciated if anyone can help.

    nvm SOLVED it..
    Last edited by mx70kc; February 1st 2009 at 04:04 PM. Reason: solved
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mx70kc View Post
    Hi, so i have to find the probability in a random sample to find that the average lies between 475 and 540 with mean 500 and st.dev 125. the z-values i got for 475 is -1 and for 540 1.6. I look on the z-table to find that the p-value for -1 is 0.1587 and 1.6 0.05487.

    The sum of those two is 0.2135 and that would be the probability right? but the answer sheet says its 0.7865. what did i do wrong? greatly appreciated if anyone can help.

    nvm SOLVED it..
    nice!
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