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Standard Deviation homework

  1. Feb 18, 2004 #1
    Help please??

    To anybody that can offer a hand.

    <x>=5, Standard Deviation = 2, median Mx=4.5, Quartile1=4, Quartile 2=6, xmin=0, xmax=9.

    After a linear tranform: y= -2x+1. What are <y>, Standard deviation y, median y, Q1y, Q2y, Ymin, Ymax.

    I was given this equation for homework and I am totally lost.
  2. jcsd
  3. Feb 18, 2004 #2


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    Except for the standard deviation, all the items you want can be botained by simply applying the linear transformation to an x quantity to get the corresponding y quantity. For example <y>=-2<x>+1. To get the standard deviation, you multiply by the absolute value of the multiplicative constant, therefore y standard deviation is 4.
  4. Feb 19, 2004 #3

    matt grime

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    Re: Help please??

    you know how you've got all the formulae for workingout those quantities? we,, instead of putting an x in the, try putting ax+b and seeing what the answer is and how it relates to the untransformed quantity:

    mean: [tex]E:=\sum_nx_i/N[/tex] where N is the number of measurements (or whatever) transform by ax+b [tex]\sum_n(ax_i+b)/N=a\sum_nx_i/N +\sum_nb/N = b+ a\sum_nx_i/N = b+aE[/tex]
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