In the Keynesian model, suppose the Fed wants to keep output unchanged. If the IS curve shifts to the left, and the Fed acts to keep output unchanged, then

What does average total cost equal?

a. change in total costs divided by quantity produced b. change in total costs divided by change in quantity produced c. (fixed costs plus variable costs) divided by change in quantity produced d. (fixed costs plus variable costs) divided by quantity produced

Let S = y - (100 + 0.75y). Assume no government or foreign sectors. At the equilibrium level of income, y* = 400, the level of investment is

A) 0. B) 75. C) 300. D) 400.