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anonymous
 2 years 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.
anonymous
 2 years 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.

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anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0what does mean E(X2i) means E(even) ?

anonymous
 2 years 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.

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0so S is sigma(i)=1100Xi is it right

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1392444372176:dw

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0but it is not the answer because the problem wants var(s) but i dont know what is exact s?

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

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1392445311784:dw

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1392445440041:dw

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1392445541588:dw

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0I can't see the right side of what you did.

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0dw:1392447809874:dw How'd you get this part?

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0all is n^2 so you have to subtract from n (x1 x2 .. xn)

anonymous
 2 years ago
Best ResponseYou've already chosen the best response.0all term in sigma without itself terms

anonymous
 2 years 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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