Addition and Subtraction

Lesson

This chapter looks at how to subtract a multiple of $10$10 from a two digit number.

What does a multiple of $10$10 look like?

Well if you have more than one $10$10 grouped together, you have a multiple of ten. $2$2 tens added together are $20$20, so $20$20 is a multiple of $10$10.

If I have $5$5 tens I had $10+10+10+10+10$10+10+10+10+10 to get $50$50, $50$50 is also a multiple of ten.

How do we subtract multiples of ten from a $2$2 digit numbers.

Well we have to consider the place values, the tens and the ones (or units).

There are $2$2 ways we could subtract the multiple of ten from the two digit number. We could take each ten away one at a time, so $32-20$32−20 is the same as $32-10-10$32−10−10.

My first step is $32-10$32−10 which is $22$22, then my next step is $22-10$22−10 which is $12$12. So $32-20=12$32−20=12.

The second way we can subtract multiples of ten is to align our 2 numbers in place values. We then subtract the ones, and then the tens. Here is what 46 - 30 looks like.

Watch the video below to see how we can do these 2 ways.

Tens | Units | |
---|---|---|

$4$4 | $6$6 | |

- | $3$3 | $0$0 |

= | $1$1 | $6$6 |

EXAMPLE 1

Find the value of $90-10$90−10?

Create a pattern by subtracting $10$10 each time.

$90$90, $\editable{}$, $\editable{}$, $\editable{}$, $\editable{}$, $\editable{}$

Complete the number sentence below to make it true.

$48-\editable{}=18$48−=18

Know forward and backward counting sequences with whole numbers to at least 1000.