Lesson video

Hello, I'm Miss Miah and I'm so excited to be a part of your learning journey today.

I hope you enjoy this lesson as much as I do.

In this lesson, you will be able to multiply a two digit number by a one digit number using short multiplication.

In this case, there will be no regrouping.

So our keywords for today are short multiplication and factor.

You may have heard of these words before and if you have, try and remember what they mean.

So a way of recording using columns to set out and calculate a multiplication is called short multiplication.

Numbers we can multiply together to get another number are known as factors, and here we can see that there's an equation.

So two multiplied by three equals six, two and three are factors.

So our first lesson cycle will consist of us understanding recording using short multiplication.

Let's begin.

In this lesson, you will meet Alex and Sofia.

Two bikes cost 43 pounds.

What is the total cost? So I want you to think about what multiplication equation is needed and what other strategies can you use to solve this problem? Have a think.

Now, you could use an informal strategy, you could use mental strategies, but today because we're focusing on short multiplication, that is what we will be using.

We can use short multiplication to multiply a two digit by a one digit number.

So on the left you can see that we've got the base 10 blocks, and on the right we've got the beginnings of our short multiplication method.

So we start by writing the largest factor first and that goes at the top.

Make sure to align your digits correctly.

So we've partitioned 43 into four tens and three ones.

Then write the smallest factor below, lining up the digits.

Again, make sure to align your digits correctly.

Now multiply starting with the ones.

So two multiplied by three ones is equal to six ones.

You're going to write six in the ones column.

Then move to the tens.

Two multiplied by four tens is equal to eight tens.

Write eight in the tens column.

Eight tens add six ones is equal to 86.

So the product is 86.

We didn't need to take any further steps because you've already got the answer.

So two bikes would cost a total of 86 pounds over to you.

So the product is 39, which short multiplication shows this correctly.

Have a think, you can pause the video here.

How did you do? If you got B, you are correct.

So because the product is 39, 39 would need to be placed underneath.

We know that 13 being the larger factor has to go at the top.

We know that three multiplied by three gives us nine ones.

Now between b and c we can see that both have 13 and three.

The three needs to be placed in the ones column.

So in this case, b is the correct answer.

Let's move on.

There are two rows of 32 chairs.

How many chairs are there altogether? So I want you to think about what multiplication equation is needed.

What other methods can we use to solve this problem? Have a think.

So in terms of methods and different strategies, we could use the grid model.

We could also use an informal written method.

We could also use a mental strategy, and I like mental strategies, especially when there's no instances of regrouping involved.

And I can see by looking at my twos and my tens and the fact that I'll be multiplying by, there are no instances of regrouping, so it probably would be more efficient for me to use a mental strategy.

However, because we are using short multiplication, that is what we're going to do to solve this equation and this will also help us practise using short multiplication as well.

So the equation that you should have got was 32 multiplied by two or two multiplied by 32.

Now we begin by writing the larger factor first.

Writing the larger factor at the top makes it easier to calculate the answer.

So we place that at the top.

You have to make sure you align your digits correctly.

This is absolutely crucial so that when it comes to actually multiplying by our ones, it's far more easier and it helps us to calculate the correct product.

Then we move on to writing the smaller factor below, lining up the digits.

So here we can see we've placed the two in the ones column.

Now we can start multiplying beginning by multiplying with the ones.

Two multiply by two ones is equal to four ones.

So we place the four in the ones column.

Then we move on to the tens.

Two multiplied by three tens is equal to six tens.

We write the six in the tens column.

The product is 64, so that means there are 64 chairs altogether.

Over to you.

If the factors are 13 and two, which short multiplication method is correct.

Have a think, you can pause the video here.

How did you do? If you got b as your answer, you are correct.

And that is because if your factors are 13 and two, 13 being the larger factor needs to be placed at the top and two being the smaller factor needs to be placed in the ones column underneath.

So that means b is the accurate representation for that question.

Back to you again.

Which short multiplication method matches the base 10 blocks and how do you know? You can pause the video here, have a go.

How did you do.

So a was the correct answer.

There are two groups of four tens and three ones.

The factors are aligned correctly.

Moving on.

Four headphones are being sold at 21 pounds each.

What is the total cost? So in this case, what is known and what is unknown? Have a think.

Well, we know that there are four headphones and they cost 21 pounds each.

We do not know the total costs.

So that is what we are going to be calculating.

We've got Sofia here who will be using the short multiplication.

So we can see here that Alex and Sofia have used two different ways to record 21 multiplied by four.

I want you to think about what is the same and what is different between both methods.

Sofia says that her recording was more efficient.

Alex has noticed that he's still got the same answer as Sofia.

So what is the same? The larger factor is at the top and the smaller factor is at the bottom.

The product is the same and the digits are aligned correctly.

However, in the expanded method, the partial products are recorded, whereas in short multiplication the partial products are not recorded.

Okay, over to you.

You are going to be using Alex's expanded recording to fill in the gaps for Sofia's short multiplication recording.

You can pause the video here, off you go.

Okay, so how did you do? Let's begin.

This is what you should have got.

So 21 multiplied by four, the larger factor going at the top and the smaller factor going at the bottom.

We do not need to record our partial products.

They've been highlighted in a different colour in the expanded multiplication.

What you should have done after that was multiplied your ones first, resulting in four, and then multiplied by your tens.

So four multiplied by two tens is eight tens.

Place that next to the four underneath the tens column and your product is 84.

Okay, so for task one.

In this lesson cycle you are going to be matching the representations to the correct short multiplication.

You can see here that you've got an equation, you've got the base 10 blocks there and you've got an expanded method of multiplication.

You are going to be matching this to the short multiplication on the other side.

So for the second task, you will be filling in the gaps to complete the short multiplication.

For the third task, you will record these as short multiplication.

You can pause the video here.

Good luck on the tasks.

How did you do? So this is what you should have got for the first task.

You can see that 22 multiplied by three is matched with the short multiplication example, with 22 being at the top, three being at the bottom aligned with the ones.

And then the answer that you should have got was 66.

The base 10 blocks have been matched with 43 multiplied by two.

We know that's correct because if we look at one group of the base 10 blocks, we've got four tens and three ones.

So we can see that's been represented in our short multiplication and it's been placed at the top.

We've got two groups of those.

So 43 multiplied by two, the answer is 86.

And lastly, we've got an expanded method of multiplication here.

This one, all we had to do was think to ourselves.

Okay, so the partial products do not need to be recorded.

Everything else stays the same.

That is the match there.

For question two and for question three, you can see the answers on the screen.

Do tick the ones that you've got correct.

If you manage to get those all correct.

Big well done.

Let's move on.

So for this second lesson cycle, we are actually going to be applying short multiplication recording.

So to begin with, bikes cost 23 pounds each.

Sofia buys two.

What is the total cost? And I want you to think about the multiplication equation needed for this.

So in this case, there are two bikes.

They cost 23 pounds.

So our multiplication equation could be two multiplied by 23 or 23 multiplied by two.

This time when it comes to recording, you can see that we've omitted, we don't have the tens and ones labelling, we've gotten rid of it.

So what we're going to start off by doing is placing the larger factor at the top 23.

So then you're going to write the smaller factor below, lining up the digits and because two is the smallest it is placed underneath.

Now multiply starting with the ones.

Two multiply by three ones is equal to six ones.

We write the six in the ones column, then move on to the tens.

Two multiplied by two tens is equal to four tens.

Write the four in the tens column, four tens, add six ones is equal to 46.

This is known as short multiplication.

So two bikes will cost 46 pounds altogether.

Now Sofia was calculating the same equation.

She got 45 as her answer.

What mistake do you think Sofia's made? What do you think? So Sofia may have added, instead of multiplying two by three ones.

In this case a number from Sofia's calculation has robbed off.

What could the missing number be? Sofia says that she can use her times table's facts to help her.

So I want you to think what is known and what is unknown.

We know that 33 is a factor.

We know that the product is 66, we are missing one factor.

So that missing factor multiplied by 33 will give us 66.

Start by looking at the ones column.

Something multiplied by three ones gives me six ones.

I know that two multiplied by three ones is equal to six ones.

So the missing factor must be two, put two in the ones column.

How can we check Sofia is correct? Have a think.

Well, you can use a mental strategy.

I know that 33 doubled is 66, or you might even know that 66 halved is 33.

Over to you.

What is the missing number? Here we have Sofia who's stating that she will look at the ones column first to help her.

You could do the same.

What I would like you to do is also explain your thinking to your partner.

Pause the video here to have a go.

How did you do? So the missing factor was three.

And we can check that because three multiply by three is nine ones and three multiply by one 10 is three tens.

Three tens at nine, ones is 39.

Back to you again.

So what are the missing numbers? We can see in this example that one of the digits from the largest factor is missing and a digit from our product is missing.

I want you to explain to your partner what the missing number is.

How will you tackle this question? Pause the video here.

Okay, so how did you do? So we know that our factor is three.

Something multiplied by three gives me a product that has three tens.

We can start off by looking at our ones first.

So three multiplied by three gives me nine ones.

Now we can move on to our tens.

If I look at the product, I can see that there are three tens there and if my factor is three, that means three multiplied by something.

Tens will give me three tens.

And I know that three multiplied by one 10 will give me three tens.

So if you got that as your answer, well done.

Okay, onto our last few tasks for this learning cycle.

For the first task, you are going to be using short multiplication to record and calculate these equations.

14 multiplied by 2, 32 multiplied by three and three multiplied by 23.

For question two, you are going to be filling in the gaps.

You are going to be finding the missing numbers.

And lastly, for question three, you are going to complete the word problem below using short multiplication.

So Lucas, Jacob, and Sofia buy caps costing different prices.

Who spent the least? In this case you can see that Jacob has bought four caps at 22 pounds, Lucas has bought two caps at 43 pounds and Sofia has bought three caps at 31 pounds.

Do remember to use short multiplication to show you are working.

You can pause the video now to start the task.

How did you do? We'll start off with question one.

So 14 being the larger factor, we should have placed this at the top with two being placed underneath.

We then multiply starting with our ones.

We know that two multiplied by four is eight ones and then two multiplied by one 10 is two tens.

Two tens at eight ones is 28.

We then move on to the second one.

So 32 is our larger factor.

We place 32 at the top and then three being our smaller factor we place that at the bottom.

Three multiplied by two ones gives us six ones, and then three multiplied by three tens gives us nine tens.

We place the nine under the tens column.

This gives us a product of 96.

And then the last question, 23 multiplied by three.

So 23 being the largest factor, we place that at the top, three being the smaller factor, we place that at the bottom.

Three multiplied by three gives us nine ones, three multiplied by two gives us six tens.

We place the six underneath the tens column and we place the nine ones underneath the ones column.

This gives us a product of 69.

For question two, have a look.

Did you get the correct answers? If you did give yourself a tick for each question.

For these, I would've definitely started off by looking at my ones column first and then use the information that I had to then slowly calculate the answers.

In order to calculate Jacob's total cost, we would be multiplying 22 by four.

So we place 22 at the top and then we place four at the bottom because it's our smallest factor and then we multiply by in our ones first.

So four multiply by two is eight ones, four multiply by two tens is eight tens.

Jacob spent 88 pounds in total.

Now Sofia bought three caps at 31 pounds.

So this is the short multiplication that you should have recorded.

The larger factor being at the top, the smaller factor being at the bottom.

We know that three multiplied by one ones is three ones, and then three multiplied by three tens is nine tens.

Make sure you align your digits correctly.

Sofia spent 93 pounds in total.

And lastly, we have Lucas who bought two caps at 43 pounds.

So we start by placing the larger factor at the top, which is 43 and then two which is our smaller factor at the bottom.

We start by multiplying our ones.

So two multiplied by three ones is six ones, and then two multiplied by four tens gives us eight tens.

Make sure you align your digits correctly when you are writing your answer.

So that means Lucas spent 86 pounds in total.

If you've got all of those answers correct, amazing job well done.

So to summarise, today we multiplied a two digit number by a one digit number using short multiplication, no regroups.

Short multiplication is one way to record the process of a multiplication calculation.

I hope you enjoyed this lesson.