Let us suppose we have two simple supply and demand equations
- Qd = 20 – 2P
- Qs = -10 + 2P
To find where QS = Qd we put the two equations together
- 20-2P = -10 + 2P
- 20+10= 4P
- 30/4=P
- P = 7.5
To find Q, we just put this value of P into one of the equations
- Q = 20 – (2×7.5)
- Q= 5

| Qd = 20 – 2P | Qs = -10 + 2P | |
| P | Qd | QS |
| 0 | 20 | -10 |
| 1 | 18 | -8 |
| 2 | 16 | -6 |
| 3 | 14 | -4 |
| 4 | 12 | -2 |
| 5 | 10 | 0 |
| 6 | 8 | 2 |
| 7 | 6 | 4 |
| 7.5 | 5 | 5 |
| 8 | 4 | 6 |
| 9 | 2 | 8 |
| 10 | 0 | 10 |
| 11 | -2 | 12 |
| 12 | -4 | 14 |
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Tejvan Pettinger studied PPE at LMH, Oxford University.