E(XY) = E(X) E(Y) if X and Y are independet. What about E(X+Y) ?
The formula E(XY) = E(X) E(Y) holds true only when X and Y are independent random variables. However, when it comes to finding the expected value of X + Y, we cannot apply the same formula because the sum of two random variables is not necessarily independent.

To calculate E(X+Y), we need to use a different approach. We can use the linearity property of expected values, which states that:

E(aX + bY) = aE(X) + bE(Y)

where a and b are constants.

Using this property, we can rewrite X+Y as 1*X + 1*Y and apply the formula:

E(X+Y) = 1*E(X) + 1*E(Y)

Therefore, the expected value of X+Y is simply the sum of their individual expected values.