Expanding: Informal Recording 1 (Subtraction 2 and 3 digits Expanded Column Method) 

Vocabulary

subtract, subtraction

take away

minus

leaves

makes

count

 

Hints and Tips

As subtraction expands to 2- and 3-digits, the need for proper alignment of numbers should be emphasised.

Keeping digits in the proper places helps prevent errors. Help your child to realise that subtracting 3-digit numbers is similar to subtracting 2-digit numbers.

If your child has a good understanding of place value, he/she will find this method less challenging. If not, using a place value chart offers a way of getting the digits in the correct places (if needed) until your child is comfortable with the concept.

Essential Prior Knowledge

Know how our place value system works.

Know the largest number comes first in subtraction.

Know how to estimate an answer.

Know that 1 of any column gives you 10 of the column to its right. (1 of these makes 10 of these)

Know how to partition and re-combine numbers.

 

Activity

The first step in learning column subtraction is to use expanded column subtraction. The numbers are written fully in columns according to their place value.

As the process for 2 and 3 digit subtraction is the same, we shall concentrate on 3 digits.

Let’s calculate 395 - 253

                   300  90  5

                  -200  50  3

                 = 100  40  2

 

With subtraction, you start with the column on the right-hand side and subtract the 3 from the 5. 5 – 3 = 2

You now subtract the 50 from the 90 in the next column to the left. 90 – 50 = 40

Finally, subtract the 200 from the 300. 300 – 200 = 100

The answer = 142

Your child will need a lot of practise to embed this skill.

It is a useful skill for your child to acquire before he/she begins to learn how to record using column subtraction.