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sleung
Group Title
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.
 6 months ago
 6 months ago
sleung Group Title
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.
 6 months ago
 6 months ago

This Question is Open

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

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

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

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392444372176:dw
 6 months ago

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

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

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392445311784:dw
 6 months ago

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392445440041:dw
 6 months ago

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392445541588:dw
 6 months ago

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

sleung Group TitleBest ResponseYou've already chosen the best response.0
How'd you get n^2n?
 6 months ago

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

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

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

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