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 11 months ago
Okay, I have another one here: Suppose that
X1,...,X100
are random variables with
E(Xi)=100,E(X2i)=10100
If
Cov(Xi,Xj)=−1,i≠j
what is Var(S), where
S=∑i=1100Xi
? I got Var(S) to be 100, which is the correct answer but what good does knowing the covariance do? I tried using it, and it just throws everything off.
 11 months ago
Okay, I have another one here: Suppose that X1,...,X100 are random variables with E(Xi)=100,E(X2i)=10100 If Cov(Xi,Xj)=−1,i≠j what is Var(S), where S=∑i=1100Xi ? I got Var(S) to be 100, which is the correct answer but what good does knowing the covariance do? I tried using it, and it just throws everything off.

This Question is Open

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1what does mean E(X2i) means E(even) ?

sleung
 11 months ago
Best ResponseYou've already chosen the best response.0It means \[E(X _{i}^{2})\] Sorry about the notation  it didn't copy and paste correctly.

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1so S is sigma(i)=1100Xi is it right

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1dw:1392444372176:dw

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1but it is not the answer because the problem wants var(s) but i dont know what is exact s?

sleung
 11 months ago
Best ResponseYou've already chosen the best response.0Sorry, \[S=\sum_{i=1}^{100}X _{i}\]

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1dw:1392445311784:dw

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1dw:1392445440041:dw

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1dw:1392445541588:dw

sleung
 11 months ago
Best ResponseYou've already chosen the best response.0I can't see the right side of what you did.

sleung
 11 months ago
Best ResponseYou've already chosen the best response.0dw:1392447809874:dw How'd you get this part?

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1all is n^2 so you have to subtract from n (x1 x2 .. xn)

mahmit2012
 11 months ago
Best ResponseYou've already chosen the best response.1all term in sigma without itself terms

sleung
 11 months ago
Best ResponseYou've already chosen the best response.0Suppose that (X,Y) is uniformly chosen from the set given by \[0<X<3, x<y<\sqrt{3x} \]Find the marginal density of Y.
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