CT3 IAI Nov 2012 sample variance

Discussion in 'CT3' started by Anjum, Mar 3, 2017.

  1. Anjum

    Anjum Member

    Question 9-Part (2)

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    While finding the missing variance I am using the formula (1/n-1)*(sum of (Xi^2)- (n*mean^2))

    Through this method i am getting the value as 0.1176
    But in the solutions they have used the formula (1/n-1)*(sum of (Xi-mean)^2) through which the solution is 0.1213

    Doubts- Should both the formulas not give the same result
    2. How to decide which formula to use
    3. Will I get marks if I use the first formula

    Thanks for your help !!!
     
  2. John Lee

    John Lee ActEd Tutor Staff Member

    Both should give exactly the same answer.

    The values are 5.193, 4.500, 4.787

    They give a sample mean of 4.827 and a sum of squares of 70.135.

    This gives:

    0.5(70.135 - 3*4.827^2) = 0.1213
     

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