Monopoly
Monopoly:  Demand and marginal revenue curve

The firm's marginal revenue (MR) is the change in total revenue when one extra unit of output is sold and is given in column 4.  

Because MR is the change in total revenue resulting from the sale of of an extra unit of output, it applies to the movement from one unit to the next, rather than a specific unit.  The value of MR is therefore plotted  between the two units concerned, rather than to specific unit.  

 
Quantity 
(units)
Q
Price (P) and average revenue (AR)
(R)
Total revenue TR
(PxQ)
(R)
Marginal revenue
MR
(R)
1 8 8
2 7 14
3 6 18
4 5 20
5 4 20

6

3

18