This question gave me a table with values for $x$ and $y$ below:
The question is find $ E(XY)$
Because they are discrete random variables, I got the general form :
$$\ \sum_{y=0}^{2}\sum_{x=0}^{2} xyf(x,y)$$
From this, I struggled with putting values in.
I start by ignoring the outside sum, focusing on just $y$.
$y=0$ I multiply 0 and 0.25. 0.25 being $f(y)$
For $y=1$, I get $1*0.30 = 0.3$
$y=2, 2*0.45 =0.45$
I go to check the mark scheme to make sure I'm on track and the Y summation is completely wrong and they use $x$. Why is this?