Ch11 practice qs 11.4i

Discussion in 'SP8' started by sma09gc, Aug 29, 2019.

  1. sma09gc

    sma09gc Member

    Probably a very simplistic question but I can’t find the answer anywhere on google or in any old notes that I have, but how has E(X^3) been calculated, without knowing the distribution of X?

    Also, in part 2, where have the simultaneous equations come from? These are different to the translated gamma formulae and I’m now sure why?

    Thanks!
     
    Last edited by a moderator: Aug 29, 2019
  2. Darren Michaels

    Darren Michaels ActEd Tutor Staff Member

    E(X^3) has been calculated from the skewness E[(X-EX)^3] by multiplying out the brackets and using the values given to you in the question.

    In part 2 the equations come from the assumption given in the question that (S-a)/b is a chi squared n and using the results on page 12 of the Tables.

    For example, var [(S-a)/b]=var [S/b] = var S/b^2 and from the Tables we know that the variance of a chi-squared with n degrees of freedom is 2n.
     

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