Malaprop Ltd. sells two products. Daily sales of product A have a mean of $70 with a standard deviation of $10, while sales of product B have a mean of $200 with a standard deviation of $30. Sales of the products tend to rise and fall at the same time, having a positive covariance of 400.
(a) Find the mean daily sales for both products together.
(b) Find the standard deviation of total sales of both products.
(c) Is the variance of the total sales greater than or less than the sum of the variances for the two products?