Column subtraction
You learn to subtract big numbers in columns, and to exchange when a column does not work.
How to work it out
- Line up ones under ones.
- Start on the right and subtract bottom from top.
- If not possible, borrow 1 ten from the column to the left.
115
425
−218
207
425 − 218
- Ones: 5 − 8 does not work, so exchange a ten: 15 − 8 = 7.
- Tens: the 2 has become 1, and 1 − 1 = 0.
- Hundreds: 4 − 2 = 2.
- The answer is 207.
More examples
812 − 347
- Ones: 2 − 7 does not work, so exchange a ten: 12 − 7 = 5.
- Tens: the 1 has become 0, and 0 − 4 does not work, so exchange a hundred: 10 − 4 = 6.
- Hundreds: the 8 has become 7, and 7 − 3 = 4.
- The answer is 465.
71012
812
−347
465
500 − 263
- The 0 in the tens has nothing to give, so exchange from the 5: it becomes 4, the tens become 9 and the ones become 10.
- Ones: 10 − 3 = 7.
- Tens: 9 − 6 = 3.
- Hundreds: 4 − 2 = 2.
- The answer is 237.
4910
500
−263
237