Refer to Exercise 6.7. Find the variance of (X + Y) . Within what range would you

Question:

Refer to Exercise 6.7. Find the variance of (X + Y) . Within what range would you expect (X + Y) to fall?

Data from Exercise 6.7

A special delivery truck travels from point A to point B and back over the same route each day. There are three traffic lights on this route. Let X be the number of red lights the truck encounters on the way to delivery point B and let Y be the number of red lights the truck encounters on the way back to delivery point A. A traffic engineer has determined the joint probability distribution of X and Y shown in the table.