Q, or Q = 90.
Q, where Q is the total output. Compare the Nash equilibrium of Cournot's model with the competitive outcome and the monopoly outcome.
We know that in the unique Nash equilibrium each firm's output is 30.
In a long run competitive equilibrium the price is equal to the minimum average cost, which is 30. Thus the total output of the firms is Q such that 30 = 120 Q, or Q = 90.
A monopolist chooses the output for which MC is equal to MR. We have TR(y) = y(120 y), so MR(y) = 120 2y. Thus the monopolist's output y satisfies MC(y) = 30 = 120 2y, or
y = 45.
In summary, the three outcomes are given in the following table.
| Total output | Price | |
| Competition | 90 | 30 |
| Duopoly | 60 | 60 |
| Monopoly | 45 | 75 |