# Thread: Help with problem on expected value, covariance, and mean of linear function

1. ## Help with problem on expected value, covariance, and mean of linear function

I attached a picture of the problem I am having trouble with.

I know how to do a (just add the rows and columns).

I'm a little confused on b, c, and d. Any help would be greatly appreciated.

Thanks,

Zach

2. Ok, I read the sticky post and here's the effort I already used
(btw, this isn't a homework problem, but a practice exam)

b) I honestly have no idea. I know that the expected value of a single random variable is the sum of x * probability. My best guess here would be a sumproduct between the row total and column totals (marginal properties)

c) I have the formula for covariance is E[X - meanx)(Y - meanx)] but I don't know where to get the mean for x and the mean for y b/c the probabilities shown are for joint events

d) Isn't this just the expected value * 2?

3. I gave it some more look but I still don't know if I got it right

b) I took the expected value of x (sumproduct([1,2,3], [.17,.38,.45]) abd added it to the expected value of y (sumproduct[0,1,2],[.28,26,.46]) using the values of the marginal probability

c)I added the expected values of x and y from b

d) =(SUM(the possible values of random variable X)-expected value of x)*(SUM(possible values of random variable Y)-expected value of y)* expected value of x,y

I don't think it's right though..

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