Teacher talks: Video playlist

[MUSIC THEME]

[SCHOOL BELL RING]

Hello, I’m Mr Smith, and together we’re going to learn about adding a one digit number to numbers that have up to three digits.

I’m going to show you some clever tricks that will help you picture the sum and work out the answer when you’re adding.

Let’s start off by adding to a two-digit number.

This will help us later as the same rules apply when adding to three digit numbers.

Unless you’re crossing into another ten or hundred, it is the place value of the ones that changes.

So, how could you work out 57 add 5?

There’s 57, so, let’s count on five.

We’ve landed on 62.

So, 57 add five equals 62.

Both the tens and ones columns have changed this time because we bridged the ten when adding.

Another way you could have answered this question was by partitioning the five into the two and three.

Now you can use your number bond knowledge to get to the next ten by adding the three to 57 first.

Once you’ve reached the 60, you would just have to add on the remaining two.

Now, we’ve got that in the bag, let’s see what happens when we add a one digit number to a three digit number.

Let’s look at an example using a place value grid.

Here we have three hundreds, two tens and a one. That makes 321.

What number would we make if we added five more?

Look closely at which place value column changes as we add more ones.

Five more than 321 is 326.

Can you see how only the ones place value changes this time?

That’s because we didn’t have to cross into another ten.

Let’s look at one more example.

What is 298 add seven?

Shall we use our number line again to answer this one?

There’s 298.

So, let’s count on seven more steps.

If you wanted to try the partitioning method, you would just partition seven into two and five.

Add the two first to reach 300 and then add the five.

See how both methods get you the same answer?

298 add seven equals 305.

Look how all the digits have changed with this answer.

Can you think why? It’s because we crossed into another hundred.

Now I need your help.

Can you help me decide whether I’ve added these three digit and one digit numbers correctly?

If I have, put your thumbs up.

If you think I’m wrong, put your thumbs down.

A number line will be on the screen if you need it.

Don’t forget, you can pause the video if you need more time.

541 plus eight equals 549.

Am I correct or have I made a mistake?

Yes, I’m right.

Well done if you got your thumbs up.

OK, next one.

285 add five is 289.

Right or wrong?

Oh, no.

I’ve made a mistake.

I only counted on four, not five.

The answer should be 290.

Hope you had your thumbs down.

If not, don’t worry.

You’ve got one more to try.

Hope I get it right this time.

Is 325 add six 331?

Right or wrong?

Yes, I’m right.

If you put your thumbs up, great work.

Thanks for helping me double check my work.

Always take your time when you’re adding one digit to any amount of digits.

Double check which place values are changing too, especially if you’re crossing the tens.

Why not roll the dice to create your own two or three digit number?

Then roll again to see which one digit number you have to add on to it.