Bonjour j'aurai besoin d'un coup de pouce den proba/stat svp Voici l'exo
On considère une variable aléatoire discrète X défine par la loi de probabilité suivante :
xi , P(X=xi)
-5 , 1/4
-4 , a
1 , 1/2
2 , 1/8

1/Calculer a
2/Calculer l'espérance et la variance de X

C'est un QCM choix possible A.8.25 , B. 1/8,C.0, et D.-1

Pour 1/ je pense que la somme des P(X=xi) doit être égale à 1 donc réponse 1/8
Pour 2/ je pense qu'il faut d'abord dire qu'elle suit telle type de loi (normale ?) et après esperance = moyenne/médiane non ?

Merci beaucoup d'avance

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