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Math Help - standard deviation

  1. #1
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    standard deviation

    Some reason I get a different answer than the actual answer.

    * = Standard Deviation, which is unknown and that is what we are solving for
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by freudling View Post
    Some reason I get a different answer than the actual answer.

    * = Standard Deviation, which is unknown and that is what we are solving for
    0.20 = \frac {[0.08 + (0.13 + 0.08)]SD}{0.25} ..............multiply both sides by 0.25

    \Rightarrow 0.05 = [0.08 + 0.13 + 0.08]SD .............calculate the coefficient of SD

    \Rightarrow 0.05 = 0.29SD ...................................Now divide both sides by 0.29

    \Rightarrow SD = \frac {0.05}{0.29} = 0.1724 ...
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    Answer should be .6, but I can't quite get it.
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by freudling View Post
    Answer should be .6, but I can't quite get it.
    0.6 is not the solution to the equation you posted. double check for typos
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  5. #5
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    Sorry, my error in posting, it is:

    .20 = .08+ [(.13 - .08) * / .25] = .08+ .2 *

    * = .12/.2 = .6
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  6. #6
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by freudling View Post
    Sorry, my error in posting, it is:

    .20 = .08+ [(.13 - .08) * / .25] = .08+ .2 *

    * = .12/.2 = .6
    ok, so here we can cut out the middle man, and equate the first and last piece, we can do that since all three pieces are equal. i don't know how you ended up with this type of equation to begin with

    0.20 = 0.08 + 0.2~SD ...........subtract 0.08 from both sides

    \Rightarrow 0.12 = 0.2~SD ........divide both sides by 0.2

    \Rightarrow SD = \frac {0.12}{0.2} = 0.6


    EDIT: Oh, the last piece is what you simplified the middle piece to get. Ok. Yeah, you still do what I did for the next step
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  7. #7
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    Jhevon, you are the man. Thanks.
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