Solution - Long subtraction
12.9
Step-by-step explanation
1. Rewrite the numbers from top to bottom, aligned by their place values
| Place value | tens | ones | . | tenths |
| 2 | 0 | . | 7 | |
| - | 7 | . | 8 | |
| . |
2. Subtract the numbers using long subtraction method
Because the upper digit (7) in the tenths column is too small to get a positive difference, borrow 1 from the number to the left (20) which becomes (19) and get (17).
| Place value | tens | ones | . | tenths |
| 1 | 17 | |||
| 2 | 0 | . | 7 | |
| - | 7 | . | 8 | |
| . |
Subtract the numbers in the tenths column from the top number:
17-8=9
| Place value | tens | ones | . | tenths |
| 1 | 17 | |||
| 2 | 0 | . | 7 | |
| - | 7 | . | 8 | |
| . | 9 |
Subtract the numbers in the ones column from the top number:
9-7=2
| Place value | tens | ones | . | tenths |
| 1 | 17 | |||
| 2 | 0 | . | 7 | |
| - | 7 | . | 8 | |
| 2 | . | 9 |
Write 1 in the tens place.
| Place value | tens | ones | . | tenths |
| 1 | 17 | |||
| 2 | 0 | . | 7 | |
| - | 7 | . | 8 | |
| 1 | 2 | . | 9 |
The solution is: 12.9
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