10 balls are inserted (uniformly) into five jars ..each insertion is independent from the others.

compute E(X1*X2) where X1 and X2 describes the number of balls in each jar.

so far:

-P=Pr(Success from each jar poin of view=the ball was inserted into it)=1/5

-E(X1*X2)=E(E(X1*X2|X1))=E(X1*(10-X1)*P)=P(E(10X1-X1^2)=1OPE(X1)-E(X1^2)=10*(1/5)-10*9*((1/5)^2)+10*(1/5)) =4-90/25+2

what am i doing wrong ?

compute E(X1*X2) where X1 and X2 describes the number of balls in each jar.

so far:

-P=Pr(Success from each jar poin of view=the ball was inserted into it)=1/5

-E(X1*X2)=E(E(X1*X2|X1))=E(X1*(10-X1)*P)=P(E(10X1-X1^2)=1OPE(X1)-E(X1^2)=10*(1/5)-10*9*((1/5)^2)+10*(1/5)) =4-90/25+2

what am i doing wrong ?

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