Marginal Revenue (MR):
Marginal revenue is the change in total revenue with respect to a change in quantity sold. That is, it is the change in total revenue that results from the sale of one extra unit of the commodity. It is found by dividing the change in total revenue ( TR) by the change in quantity sold ( ΔQ).
MR = ΔTR/Q
Where ΔTR = change in TR = New TR - Old TR
ΔQ = change in Q = New Q - Old Q