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Divine Intervention
05-30-2009, 06:37
okay im having a stats exam soon and i absolutly hate stats. ive been getting worse marks in it compared to my other exams all the way from GCSEs to Uni level. anyway can anyone help me with these Covarience questions?

i know how to do E(X), E(Y), the varience questions and Cov(X,Y) but the following have me very confused:

http://img189.imageshack.us/img189/1254/cov1.jpg

for the first one i need to find Cov(Y,Ysquared) ie Cov(Y,Y^2)

for the second one i need to find Cov(X,Y|x>=14) ie Cov(X,Y given that x is greater or equal to 14).

i have the answers but dont understand how they were obtained. help appreciated and rewarded.

i hate statistics :(

EDIT: i worked out how to do Cov(Y,Y^2) --> E(Y^3)-E(Y)E(Y^2) --> 28.7 - (8.9*2.7)=2.89. so i only need help with the second one now please :):wub::wub:

EDIT: can mod change title to 50mill please considering ive done half the work already :p although worry not mathematicians, im sure to have plenty more questions and will be giving generous rewards for help PT:::
Crimson Shadow
05-30-2009, 08:27
If only I knew stats I would help you out. :(

Title changed.
Divine Intervention
05-30-2009, 10:51
thanks crimson :P guess no one will get any cash, my friend from Oxford helped me out. conditional probability its called :P

doing Cov(X,Y) as normal but ignoring the X=13 column and having the probabilities u do use divided by the sum total of them (so p(x=14 is .1/.7). god i hate stats.
Disorder
05-30-2009, 21:42
Sorry.. my wife and I looked at it and can't help. :blink:
L P
05-30-2009, 22:28
The answer is 42.

Now give me my credits, I'm broke.
Bram Gotink
06-03-2009, 07:18
The answer is 42.

Now give me my credits, I'm broke.

lol
nosejam
06-03-2009, 10:32
Weirdly enough I got both my highest and lowest marks in Stats, S1 I got 99% in, S2 I'm not sure what I got, but sub-50% I imagine.

That was a good two/three years ago and I can't really remember anything, just some very basic stuff that applies to quantum physics, which just involves normalising some wave functions and getting expectation values.
Divine Intervention
06-03-2009, 11:11
well doesnt matter any more, had my stats exam, think it went fine :P
*fingers crossed*
FeaRLezZoN3
06-03-2009, 13:45
Man i am soo happy I didnt go to college....I have no clue wtf those numbers and x's mean lol:P
nosejam
06-03-2009, 13:47
Man i am soo happy I didnt go to college....I have no clue wtf those numbers and x's mean lol:P

Could've done Geography, the only entrance requirement is you have to be able to stay within the lines when colouring in.
FeaRLezZoN3
06-03-2009, 13:49
Could've done Geography, the only entrance requirement is you have to be able to stay within the lines when colouring in.

if thats the case I would have not entered, I fall asleep when I use to color as a kid