| 20 | × | 200 | ( | 1 | − | 20 100 | ) | + | 10 | × | 400 | ( | 1 | − | a | ) | = | 6000 |
| Left side of the equation = | 4000 | ( | 1 | − | 20 100 | ) | + | 4000 | ( | 1 | − | a | ) |
| 4000 | ( | 1 | − | 20 100 | ) | + | 4000 | ( | 1 | − | a | ) | = | 6000 |
| Left side of the equation = | 4000 | × | 1 | − | 4000 | × | 20 100 | + | 4000 | ( | 1 | − | a | ) |
| = | 4000 | − | 800 | + | 4000 | ( | 1 | − | a | ) |
| = | 3200 | + | 4000 | ( | 1 | − | a | ) |
| = | 3200 | + | 4000 | × | 1 | − | 4000 | a |
| = | 3200 | + | 4000 | − | 4000 | a |
| = | 7200 | − | 4000 | a |
| 7200 | − | 4000 | a | = | 6000 |
| - | 4000 | a | = | 6000 | − | 7200 |
| - | 4000 | a | = | - | 1200 |
| 1200 | = | 4000 | a |
| 4000 | a | = | 1200 |
| a | = | 1200 | ÷ | 4000 |
| = | 1200 | × | 1 4000 |
| = | 3 | × | 1 10 |
| a | = | 3 10 |
| a | = | 0.3 |