Corrigé du 71 P. 452

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a. $\operatorname E(Y) = np = 20\times 0,3 = 6$;
$\operatorname V(X) = np(1-p) = 6\times 0,7 = 4,2$.

b. $\operatorname E(Y) = np = 50\times 0,3 = 15$;
$\operatorname V(X) = np(1-p) = 15\times 0,7 = 10,5$.

c. $\operatorname E(Y) = np = 50\times 0,55 = 27,5$;
$\operatorname V(X) = np(1-p) = 27,5\times 0,45 = 12,375$.

d. $\operatorname E(Y) = np = 120\times 0,213 = 25,56$;
$\operatorname V(X) = np(1-p) = 25,56\times 0,787 = 20,11572$.

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