COR. 01

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$\operatorname E(X) = \dfrac 12 \times (-4) + \dfrac 13 \times 7 + \dfrac 1{12}\times 12 + \dfrac 1{12}\times 20 = 3$.

$\operatorname V(X) = \dfrac 12(-4-3)^2 + \dfrac13(7-3)^2 + \dfrac1{12}(12 - 3)^2 + \dfrac1{12}(20-3)^2$
$= \dfrac{182}3 \approx 60,67$.

$\sigma(X) = \sqrt{\dfrac{182}3} \approx 7,79$.

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code : 3154