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November 26th, 2017, 04:49 AM  #1 
Member Joined: Jan 2016 From: Blackpool Posts: 95 Thanks: 2  Joint probability density question:
The joint random variables have a density \[f(x,y)=x+y\] for 0<x<1 and 0<y<1 and 0 otherwise, Evaluate E(X) and E(XY) My answer for E(x)=7/12 however i feel like i may have made a mistake somewhere. Last edited by Jaket1; November 26th, 2017 at 05:28 AM. 
November 26th, 2017, 05:50 AM  #2 
Member Joined: Jan 2016 From: Blackpool Posts: 95 Thanks: 2 
for E(XY) i got 1/3

November 26th, 2017, 10:13 AM  #3 
Senior Member Joined: Sep 2015 From: USA Posts: 1,977 Thanks: 1026 
$E[X]=\dfrac {7}{12}$ is correct Do you see any reason $E[Y] \neq E[X]$ ? $E[X Y] = \dfrac 1 3$ is also correct. 

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density, joint, probability, question 
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