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S1: Discrete Random Variable... How to find the variance? watch

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    I don't understand question d)i) Where it asks me to find the variance. I found the Var(X) and the mean of Y. But I don't understand the markscheme where it asks me to find the Var(Y). It's been a long time and I have forgotten the techqiue.

    According to the markscheme, you multiply the square of 4 by the var(X). But why do you square the 4????
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    (Original post by Future_Dr)
    I don't understand question d)i) Where it asks me to find the variance. I found the Var(X) and the mean of Y. But I don't understand the markscheme where it asks me to find the Var(Y). It's been a long time and I have forgotten the techqiue.

    According to the markscheme, you multiply the square of 4 by the var(X). But why do you square the 4????
    Don't you have a result in your textbook that says Var(aX + b) = a^2 Var(X) , where a and b are constants?
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    (Original post by Future_Dr)
    I don't understand question d)i) Where it asks me to find the variance. I found the Var(X) and the mean of Y. But I don't understand the markscheme where it asks me to find the Var(Y). It's been a long time and I have forgotten the techqiue.

    According to the markscheme, you multiply the square of 4 by the var(X). But why do you square the 4????
    Generally, Var(2x) = 2^2 Var(X)

    Similarly, Var(Y) = Var(4X+2) = 4^2 Var(X)
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    Thanks guys.


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Updated: April 1, 2013
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