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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.
 10 months ago
 10 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.
 10 months ago
 10 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) ?
 10 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.
 10 months ago

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
oh got
 10 months ago

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

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392444372176:dw
 10 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?
 10 months ago

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

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

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

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

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

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

sleung Group TitleBest ResponseYou've already chosen the best response.0
dw:1392447809874:dw How'd you get this part?
 10 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)
 10 months ago

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
all term in sigma without itself terms
 10 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.
 10 months ago
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