Use the following information on a hypothetical short-run production function to answer questions a-c

Units of Labor/Day 5 6 7 8 9
Units of Output/Day 120 140 155 165 168

The price of labor is $20 per day. Ten units of capital are used each day, regardless of output level. The price of capital is $50 per unit.

a. Calculate the marginal and average variable product of each unit of labor input.
b. Calculate total, average total, average variable, and marginal costs.
c. Can you tell where diminishing marginal returns sets in?

a. b.
Labor Output MP AP TC ATC AVC MC
5 120 -- 24 $600 $5 $0.83 --
6 140 20 23.3 $620 $4.43 $0.86 $1
7 155 15 22.14 $640 $4.13 $0.9 $1.33
8 165 10 20.63 $660 $4 $0.97 $2
9 168 3 18.67 $680 $4.05 $1.07 $6.67

c. Diminishing marginal returns sets in at some point prior to the 5th unit of labor. Note that MP is declining for 5-9 units of labor.