What is Column Subtraction?

Tiffany Maths dress

Tiffany likes maths and loves to learn how to calculate. She likes to wear her numbers dress when she is learning maths.

Tiffany has been learning column subtraction

Did you know?

Column subtracting is very useful if you need to take one number away from another number and you are unable to use mental subtraction.

When you subtract one number from another, the answer will always be a smaller number.

To do column subtraction correctly it is important that you understand place value and put each number in the correct column.

 

Subtracting numbers using column subtraction

Simple Column Subtraction

Our sum is 35 – 24

The number 35 has 3 tens and 5 ones and the number 24 has 2 tens and 4 ones, 

In order to subtract 24 from 35 we have to put the numbers in columns with the tens in one column and the ones in another.

Column Subtraction

Subtract the two numbers in the ones column first. 5 – 4 = 1 so the number 1 is placed in the = and in the ones column.

Next subtract the two numbers in the tens column. 3 – 2 = 1 so the number 1 is placed in the = and in the tens column. 

The answer is 1 ten and 1 one or 11

Column Subtracting with Regrouping (Exchanging, Borrowing)

Our sum is 45 -28

The number 45 has 4 tens and 5 ones, the number 28 has 2 tens and 8 ones

In order to subtract 28 from 45 we have to put them in columns with the tens in one column and the ones in another.

45-28

Starting with the ones column we have to subtract 8 from 5, but we cannot do this because 5 is a smaller number than 8.

We therefore have to regroup or make an exchange. We can exchange one ten for ten ones. We then have to regroup by reducing the 4 tens to 3 and adding 1 ten to the 5 ones making 15.

It is now possible to complete the subtraction – 15 – 8 = 7 and 3 – 2 in the tens column is 1. The answer to 45 – 28 is 17.

Column subtraction with regrouping and exchange

The following image shows how exchanging/regrouping works with bigger numbers and multiple regroupings.

 

Tiffany has learned enjoyed learning about column addition. She summed up her learning with the following keywords: 

addition, carrying, column, equals, hundreds, ones, place value, regrouping, tens