Solution - Long subtraction
18.9
Step-by-step explanation
1. Rewrite the numbers from top to bottom, aligned by their place values
| Place value | tens | ones | . | tenths |
| 2 | 1 | |||
| - | 2 | . | 1 | |
| . |
Put zeros in the blank number places:
| Place value | tens | ones | . | tenths |
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| . |
2. Subtract the numbers using long subtraction method
Because the upper digit (0) in the tenths column is too small to get a positive difference, borrow 1 from the digit (1) in the next number place which becomes (0) and get (10).
| Place value | tens | ones | . | tenths |
| 0 | 10 | |||
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| . |
Subtract the numbers in the tenths column from the top number:
10-0-1=9
| Place value | tens | ones | . | tenths |
| 0 | 10 | |||
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| . | 9 |
Because the upper digit (0) in the ones column is too small to get a positive difference, borrow 1 from the digit (2) in the next number place which becomes (1) and get (10).
| Place value | tens | ones | . | tenths |
| 1 | 10 | |||
| 0 | 10 | |||
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| . | 9 |
Subtract the numbers in the ones column from the top number:
10-2=8
| Place value | tens | ones | . | tenths |
| 1 | 10 | |||
| 0 | 10 | |||
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| 8 | . | 9 |
Write 1 in the tens place.
| Place value | tens | ones | . | tenths |
| 1 | 10 | |||
| 0 | 10 | |||
| 2 | 1 | . | 0 | |
| - | 2 | . | 1 | |
| 1 | 8 | . | 9 |
The solution is: 18.9
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