Math Core

Counting on helps you add. To take away, you can go the other way. Start at the big number and count back.

Count back

What is $12 - 3$ ?

Start at 12. Count back 3 numbers:

12 … 11, 10, 9

You said 3 numbers. You landed on 9. So $12 - 3 = 9$ .

Count back

To subtract a small number, say the first number. Then count down one number for each thing you take away. The last number you say is the answer.

Picture it

Here are 12 cookies. 3 get eaten.

🍪🍪🍪🍪🍪🍪🍪🍪🍪 ❌❌❌

Count what is left: 9 cookies. Counting back gives the same answer, and it is faster.

Worked example: Take away 2

What is $15 - 2$ ?

Say 15. Count back 2: 14, 13.

$15 - 2 = 13$ .

Worked example: Birds fly away

There are 11 birds. 4 fly away. How many are left?

Say 11. Count back 4 and use your fingers: 10, 9, 8, 7.

$11 - 4 = 7$ . There are 7 birds left.

Worked example: Cross over 10

What is $13 - 5$ ?

Say 13. Count back 5: 12, 11, 10, 9, 8.

$13 - 5 = 8$ .

Common mistake

Don't count the starting number. For $12 - 3$ , say "12" and then 11, 10, 9. If you say "12, 11, 10," you will be off by one.

Tip

Counting back works best when you take away a small number, like 1, 2, 3 or 4.

Practice

Practice 1

What is $9 - 2$ ?

Type a number.

Practice 2

What is $13 - 3$ ?

Type a number.

Practice 3

There are 14 ducks in a pond. 2 swim away. How many ducks are left?

Type a number.

Practice 4

What is $17 - 2$ ?

Type a number.

Practice 5

What is $12 - 4$ ?

Type a number.

Practice 6

Leo finds $10 - 3$ . He counts back: "9, 8, 7." What is the answer?

Practice 7

What is $20 - 3$ ?

Type a number.