Column subtraction step by step, for parents who learnt it differently
If you learnt to “borrow and pay back”, today’s column subtraction can look a bit different. The good news is it’s the same idea, just explained in a way that makes more sense. Here’s how your child is likely being taught it.
The words schools use
- Exchanging (not borrowing): swapping 1 ten for 10 ones, or 1 hundred for 10 tens.
- Ones, tens, hundreds: children say “ones”, not “units”.
- Subtract, take away and minus all mean the same thing. That can be confusing, so it helps to say it.
A worked example: 532 − 278
- Line the numbers up so the ones, tens and hundreds are in columns. The bigger number goes on top. Always start with the ones, on the right.
- Ones: 2 − 8. We can’t take 8 from 2, so we exchange 1 ten for 10 ones. The 3 tens become 2 tens, and the 2 ones become 12 ones. 12 − 8 = 4.
- Tens: 2 − 7. We can’t take 7 from 2, so we exchange 1 hundred for 10 tens. The 5 hundreds become 4 hundreds, and the 2 tens become 12 tens. 12 − 7 = 5.
- Hundreds: 4 − 2 = 2.
- The answer is 254.
The tricky one: zeros
Zeros cause the most trouble. Take 400 − 158.
In the ones column, 0 − 8 needs an exchange, but there are no tens to exchange. So we go to the hundreds first: 4 hundreds become 3 hundreds and 10 tens. Then we exchange 1 of those tens: 10 tens become 9 tens, and the ones become 10.
Now it’s easy: 10 − 8 = 2, 9 − 5 = 4, 3 − 1 = 2. The answer is 242.
A quick way to picture it: 400 is the same as 3 hundreds, 9 tens and 10 ones.
Common slips, and how to help
- Taking the smaller digit from the bigger one (doing 8 − 2 instead of exchanging). Ask: “Which number is on top?”
- Forgetting to cross out after an exchange. Encourage your child to always change the top number.
- Columns drifting. Squared paper keeps the digits lined up, and helps a lot with dyslexia.
- Starting on the left. Column methods always start with the ones.
If your child is stuck, use real objects. Coins work well: swap a £1 coin for ten 10p coins to show exactly what exchanging means.
How Steady Sums can help
Arithmetic World in Steady Sums practises column subtraction from the Year 3 methods up to the bigger numbers in the SATs. If your child gets stuck, a method card shows the steps, and “Show me how” walks through a question one step at a time, exactly the way schools teach it.