Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing
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.
 9 months ago
 9 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.
 9 months ago
 9 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) ?
 9 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.
 9 months ago

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

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
dw:1392444372176:dw
 9 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?
 9 months ago

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

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

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

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

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

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

sleung Group TitleBest ResponseYou've already chosen the best response.0
dw:1392447809874:dw How'd you get this part?
 9 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)
 9 months ago

mahmit2012 Group TitleBest ResponseYou've already chosen the best response.1
all term in sigma without itself terms
 9 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.
 9 months ago
See more questions >>>
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.