Fixed and variable costs. In some mass production settings there is a linear relationship between the number x of units of a product in a production run and the total cost y of making these x units.

(a) Write a population regression model to describe this relationship.

(b) Which parameter in your model is the fixed cost (for example, the cost of setting up the production line) that does not change as x increases?

(c) Which parameter in your model shows how total cost changes as more units are produced? Do you expect this number to be greater than 0 or less than 0?

(d) Actual data from several production runs will not fit a straight line exactly. What term in your model allows variation among runs of the same size x?