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Math Help - i need standard deviation help

  1. #1
    benimted
    Guest

    i need standard deviation help

    i need to do standard deviation on my calculator for my math class, but whenever i do it i get a wrong answer.

    here is what i am doing
    i enter the numbers in L1 and their frequency in L2 and then i do the formula

    ex. 10,20,30,40,50,60 in L1
    1,1,1,1,1,1 in L2

    stdDev(L1L2)= 18.70828693
    but the actual answer is 17.1
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  2. #2
    MHF Contributor

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    Now I know next to nothing about calculators.
    But 18.7 is the sample standard deviation, whereas 17.07 is the population standard deviation.
    In some computer algebra systems the difference is Stdev() with a capital S and the other is stdev(), small s.
    Look in your manual to see if the calculator does something similar.
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  3. #3
    Junior Member
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    Bump that ^

    You have population Standard deviation.

    X = 10 , 20 , 30 , 40 , 50 , 50
    Pr(X=x) 1/6, 1/6, 1/6, 1/6, 1/6, 1/6

    Because Σ Pr(X=x) = 1 (sum of all probability = 1)

    Standard deviation = σ = root(E(x^2) [E(x)]^2)

    E(x) = mean so simply (10+20+30+40+50+60) / 6 = 35

    E(x^2) = 10^2*1/6 + 20^2*1/6 + 30^2*1/6 + 40^2*1/6 + 50^2*1/6 + 60^2*1/6 = 1516.67

    σ = root(E(x^2) [E(x)]^2) = root(1516.67 35^2) = 17.0783 = 17.1

    Population standard deviation would take a while to work out XD
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