Subtraction with Regrouping

What Is Regrouping in Subtraction?#

In subtraction, regrouping means borrowing from the next place value column. We regroup when the digit being subtracted is bigger than the digit on top. When that happens, we need to borrow 1 ten (or 1 hundred) from the next column and break it into 10 smaller units.

Why Do We Need to Borrow?#

Imagine you have 4 single blocks and you need to take away 7. You cannot do that — 4 - 7 dös not work with regular counting! But if you can break one of the tens rods into 10 single blocks, then you have 14 ones. Now 14 - 7 = 7. That is regrouping!

A Simple Example: 43 - 28#

  43
- 28
----

Step 1 — Ones column: 3 - 8. We cannot do this! 3 is less than 8.

Regroup: Go to the tens column. Borrow 1 ten from the 4 tens.

• The 4 tens becomes 3 tens.
• The 1 borrowed ten becomes 10 extra ones.
• 3 ones + 10 ones = 13 ones.

Step 2 — Ones column (now): 13 - 8 = 5. Write 5.

Step 3 — Tens column: 3 - 2 = 1. Write 1.

Answer: 15 ✓

Check: Dös 15 + 28 = 43?#

15 + 28: 5+8=13, write 3 carry 1. 1+2=3, plus 1=4. Answer: 43. ✓ Correct!

Key Words for Subtraction#

In word problems, these words tell you to subtract:

• difference, fewer, less, how many more, how many left, take away, remain

Regrouping in subtraction takes practice, but once you understand why we borrow, it makes perfect sense!