| ( | 12 | − | 9 | ) | × | 80 100 | x | + | ( | 10 | − | 9 | ) | ( | 1 | − | 80 100 | ) | x | − | 1 10 | x | = | 25000 |
| Left side of the equation = | 12 | × | 80 100 | x | − | 9 | × | 80 100 | x | + | ( | 10 | − | 9 | ) | ( | 1 | − | 80 100 | ) | x | − | 1 10 | x |
| = | 48 5 | x | − | 36 5 | x | + | ( | 10 | − | 9 | ) | ( | 1 | − | 80 100 | ) | x | − | 1 10 | x |
| = | 23 10 | x | + | ( | 10 | − | 9 | ) | ( | 1 | − | 80 100 | ) | x |
| = | 23 10 | x | + | 10 | ( | 1 | − | 80 100 | ) | x | − | 9 | ( | 1 | − | 80 100 | ) | x |
| = | 23 10 | x | + | 10 | × | 1 | x | − | 10 | × | 80 100 | x | − | 9 | ( | 1 | − | 80 100 | ) | x |
| = | 23 10 | x | + | 10 | x | − | 8 | x | − | 9 | ( | 1 | − | 80 100 | ) | x |
| = | 43 10 | x | − | 9 | ( | 1 | − | 80 100 | ) | x |
| = | 43 10 | x | − | 9 | × | 1 | x | + | 9 | × | 80 100 | x |
| = | 43 10 | x | − | 9 | x | + | 36 5 | x |
| = | 5 2 | x |
5 2 | x | = | 25000 |
| x | = | 25000 | ÷ | 5 2 |
| = | 25000 | × | 2 5 |
| = | 5000 | × | 2 |
| x | = | 10000 |