A restaurant serves three fixed-price dinners costing $12, $15, and $20. For a randomly selected couple dining at this restaurant, let X be the cost of the man's dinner and Y be the cost of the woman's dinner. The joint distribution of the discrete random variables X and Y is displayed in the table below:
| | Y=12 | Y=15 | Y=20 |
|---|------|------|------|
| X=12 | 0.05 | 0.05 | 0.10 |
| X=15 | 0.05 | 0.10 | 0.35 |
| X=20 | 0 | 0.20 | 0.10 |
i) Compute the marginal distributions of X and Y and their expected values.
ii) Determine the distribution P(Z) of the total cost for dinner Z=X+Y.
iii) Compute E(Z) from the distribution in ii) and compare it to the sum E(X)+E(Y).
iv) Compute the covariance and correlation coefficient between X and Y.