81 100 | = | ( | 47 20 | − | 7 25 | − | a | ) | ÷ | 2 |
| Right side of the equation = | 47 20 | × | 1 2 | − | 7 25 | × | 1 2 | − | a | × | 1 2 |
| = | 47 40 | − | 7 50 | − | a | × | 1 2 |
| = | 207 200 | − | 1 2 | a |
81 100 | = | 207 200 | − | 1 2 | a |
1 2 | a | = | 207 200 | − | 81 100 |
1 2 | a | = | 9 40 |
| a | = | 9 40 | ÷ | 1 2 |
| = | 9 40 | × | 2 |
| = | 9 20 | × | 1 |
| a | = | 9 20 |
| a | = | 0.45 |