Number (add/sub)

Hong Kong

Stage 1

Lesson

Here we will use patterns in subtraction to help us find the difference between a two-digit and single-digit number.

Sometimes, you can partition or split the tens number to help. For example, 16 is the same as one ten and 6 ones.

Let's look at an example, can you see a pattern in the difference sum or the answers?

$16-9=7$16−9=7

$26-9=17$26−9=17

$36-9=27$36−9=27

So, in this example, we can see that when subtracting 9 from a two-digit number ending in six, you get an answer with a number ending in seven.

$12-4=8$12−4=8. Use this to find:

$22-4=\editable{}$22−4=

$32-4=\editable{}$32−4=

$42-4=\editable{}$42−4=

$72-4=\editable{}$72−4=

Complete the pattern below.

$\editable{}$ $11$11 $\editable{}$ $15$15