Addition and subtraction with regrouping: a parent guide

Regrouping is what many adults learned as "carrying" in addition and "borrowing" in subtraction. Schools now call it regrouping because it describes what actually happens: ten ones are swapped for one ten, or one ten is swapped for ten ones.

Adding with regrouping

Example: 47 + 38.

1. Add the ones: 7 + 8 = 15.
2. 15 ones is 1 ten and 5 ones. Write 5 in the ones place and carry the 1 ten to the tens column.
3. Add the tens: 4 + 3 + 1 = 8 tens.
4. The answer is 85.

Subtracting with regrouping

Example: 52 − 27.

1. Look at the ones: 2 − 7. There are not enough ones.
2. Take 1 ten from the 5 tens. That leaves 4 tens, and the 2 ones become 12 ones.
3. Subtract the ones: 12 − 7 = 5.
4. Subtract the tens: 4 − 2 = 2.
5. The answer is 25.

Regrouping across zeros

In Grade 3, children meet problems like 300 − 146. There are no tens to take from, so they regroup twice: 3 hundreds become 2 hundreds and 10 tens, then 1 of those tens becomes 10 ones. The problem is now 2 hundreds, 9 tens and 10 ones minus 1 hundred, 4 tens and 6 ones. The answer is 154.

Common mistakes

• Taking the smaller digit from the larger one in each column. For 52 − 27, a child might write 35 because 7 − 2 = 5.
• Forgetting to add the carried ten.
• Lining up digits in the wrong columns.

Make it concrete first

Use base-ten blocks, bundles of 10 straws, or coins (dimes and pennies). Let your child physically swap one ten for ten ones. Once they can do it with objects, the written steps make sense.