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    I am told to find the standard deviation of this data x 11 13 15 20 25

    I know that standard deviation is the square rooting of the variance but how would you go about this bearing in mind in includes x's?
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    what was the standard diviation ? and what exactly are you trying to find out x or the varience?
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    you may have to find the standard deviation in terms of x? Unless there's any other information given so that you can actually work out x using that?
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    Sum them all up, you should get something like:

    A + x

    Where A is a real number.

    Then divide that number by the total of numbers of values you have, in your case it is 6 giving you something like this giving you the mean..

    \mu = \dfrac{A}{6}+\dfrac{x}{6}

    Then for each value from your set of values, subtract the mean and square the value you get. For these set of values, we will call them squared values.

     x_1=x, x_2=11, x_3=13 \cdots

                             

                          (x_1-\mu)^2 = (x - (\dfrac{A}{6}+\dfrac{x}{6}))^2

                          (x_2-\mu)^2 = \cdots

                          \cdots

    Add the squared values all up and then work out the mean of the squared values by dividing by 6... This is your variance...

      \sigma^2 = \dfrac{1}{6}((x_1-\mu)^2+(x_2-\mu)^2+(x_3-\mu)^2 +\cdots)

    Then square root that value and you have you standard deviation, you should end up with an algebraic equation.
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    I've just been looking at this

    http://statistics.about.com/od/Descr...-Deviation.htm

    It tells me that you can come up with a good estimate for sd by range divided by 4.

    An estimate then would be (25-x)/4

    Is that any use to you?
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    Posted from TSR Mobile

    Thanks I worked in the end you don't use include the x.
 
 
 
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