The question is: If you know that X1 gives you 0 then what does X2 give you?

I set up a table:

**X2:**

**2**

**0**-

**2**

**X1:**

**0**0,1 0,2 0,1

**-2**0 0,3 0,3

Then I found:

Px1(0) =0,4, Px1(-2) = 0,6

Px2(2) = 0,1, Px2(0)=0,5, Px2(-2)=0,4

I know I´m supposed to use a formula for „conditional expected value“ and the formula is pX|Y=y(x) = p(x,y)/(„sum of x“ p(x,y))

but I do know understand how to do that or what „sum of x“ is or what p(x,y) is.

please help!!