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    Hi, i'm stuck on an easy question

    An automobile dealer calculates the proportion of new cars sold that have been returned variousnnumbers of times for the corrections of defects during the warranty period.

    number of returns - 0, 1, 2, 3, 4
    Proportion - 0.28, 0.36, 0.23, 0.09, 0.04

    The question is to find the variance of the numbers of returns of an automobile for corrections for defects defects during warranty?

    I found out the mean as 1.25 defects and did

    [(0-1.25)^2+(1-1.25)^2+(2-1.25)^2+(3-1.25)^2+(3-1.25)^2+(4-1.25)^2] /5

    this gives me 2.25 whereas the answer is 1.1675... any ideas would be greatly appreciated Much love in advanced.
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    (Original post by xela)
    Hi, i'm stuck on an easy question

    An automobile dealer calculates the proportion of new cars sold that have been returned variousnnumbers of times for the corrections of defects during the warranty period.

    number of returns - 0, 1, 2, 3, 4
    Proportion - 0.28, 0.36, 0.23, 0.09, 0.04

    The question is to find the variance of the numbers of returns of an automobile for corrections for defects defects during warranty?

    I found out the mean as 1.25 defects and did

    [(0-1.25)^2+(1-1.25)^2+(2-1.25)^2+(3-1.25)^2+(3-1.25)^2+(4-1.25)^2] /5

    this gives me 2.25 whereas the answer is 1.1675... any ideas would be greatly appreciated Much love in advanced.
    Var(X)=E(X^2) - E(x) ^2

    So add up x^2 *P(X=x) and subtract the square of the mean. Answer 467/400 = 1.1675 (as you said).
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    (Original post by Get me off the £\?%!^@ computer)
    Var(X)=E(X^2) - E(x) ^2

    So add up x^2 *P(X=x) and subtract the square of the mean. Answer 467/400 = 1.1675 (as you said).
    Cheers for the reply but sorry I still don't get it could you show more working and explain it to a complete n00b, thanks.
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    There's an example here.

    http://www.tutorvista.com/math/varia...andom-variable
 
 
 
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