# Probablity Question - Joint PDF Expectation/Variance

## Homework Statement

I have been given a joint PDF for X and Y, with ranges Y>X≥0.

I need to find the E(x) and E(y).

## Homework Equations

I know E(x) = ∫(x)*(f(x,y) dx and E(y) = ∫(y)*(f(x,y)) dy

## The Attempt at a Solution

For ∫x*f(x,y) dx, i used the limits = x to ∞

For ∫y*f(x,y) dy, i used the limits = 0 to y

Is this correct?

Ray Vickson
Homework Helper
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## Homework Statement

I have been given a joint PDF for X and Y, with ranges Y>X≥0.

I need to find the E(x) and E(y).

## Homework Equations

I know E(x) = ∫(x)*(f(x,y) dx and E(y) = ∫(y)*(f(x,y)) dy

## The Attempt at a Solution

For ∫x*f(x,y) dx, i used the limits = x to ∞

For ∫y*f(x,y) dy, i used the limits = 0 to y

Is this correct?

These are both wrong. EX = int x*f(x,y) dx dy, etc.

RGV

Im confused by what you meant above, but i meant to say;

I have found f(x) by ∫f(x,y) dy, with the limits x to ∞.

To then find the E(x) do i ∫x * f(x) dx, with the limits 0 to y?

Ray Vickson