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Math Help - standard deviation

  1. #1
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    standard deviation

    i hope this is in the right place but can someone please help me with this,

    if the standard deviation of X is 15 , what would be the standard deviation of 5X ?

    all help is greatly appreciated
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by percyt View Post
    i hope this is in the right place but can someone please help me with this,

    if the standard deviation of X is 15 , what would be the standard deviation of 5X ?

    all help is greatly appreciated
    How has the standard deviation of a random variable been defined for you?

    CB
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  3. #3
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    Quote Originally Posted by percyt View Post
    i hope this is in the right place but can someone please help me with this,

    if the standard deviation of X is 15 , what would be the standard deviation of 5X ?

    all help is greatly appreciated
    You're expected to know that Var(aX + b) = a^2 Var(X) and therefore sd(aX + b) = |a|sd(X).
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    mr fantastic , thank you ill have a look at that
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  5. #5
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    Quote Originally Posted by percyt View Post
    mr fantastic , thank you ill have a look at that
    Before you edited a perfectly good reply to CB to what I have, unfortunately, had to quote (and which, to be honest, is useless compared to what you had originally posted in reply to CB), what you said contained important information. Next time post the whole problem.

    From what you said before deleting it, the sd deviation you're talking about cannot be calculated without knowing the values of X. Then apply the usual formula to the data. Formulas can be found using Google.

    Thread closed.
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