Lesson video

Hello, I'm Miss Mia 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'll be able to use known facts from the 10 times tables to solve problems involving the nine times tables.

And you can see your keyword on the screen now and I'd like you to repeat it after me.

So I say array.

Fantastic, let's find out what this word means.

An array is the layout of items such as objects, numbers, arranged in rows and or columns.

You may have come across a arrays in previous lessons.

Now this lesson is all about our nine times tables and our first lesson is all to do with using known facts.

Our second lesson cycle will then be focused on solving problems. In learning today, we are going to be joined by Jacob and Sofia.

So let's get started.

Now, multiples of 10 can be shown on a number line, so you can see that it is a stack number line, at the top, we've got zero up to 12, and we are going to be chanting our multiples of 10.

So let's start with zero.

Are you ready? Let's go.

Zero, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120.

What do you notice about the multiples of 10? Multiples of 10 have a zero in the ones place.

Adjacent multiples are 10 apart or in other words they have a difference of 10.

Now you can use facts from the 10 times tables to help you calculate the nine times tables.

Jacob wants to calculate nine times three.

It's okay if you don't know that fact yet, Jacob.

We can use 10 times three.

So Sofia makes an array to show Jacob.

So here we've got 10 groups of three, but remember Jacob wants to calculate nine groups of three.

So what do you think we need to do? Well, Sofia changes the array to show the expression Jacob wants to calculate.

In other words, she's removed one group of three.

So now she can see three groups of nine.

What's the same and what's different? Well each group is one less.

There are three groups, so the whole is three less.

We started with three groups of 10, which we can write as 10 times three.

To make my array nine times three, we made each group one less.

We subtracted three counters.

So three groups of 10 minus three is equal to three groups of nine.

So our mixed operation equation to show this is 10 times three subtract three is equal to nine times three.

Now Sofia explains it in a different way.

Three groups of 10 is the same as 10 groups of three.

We can see 10 columns of three counters.

So three groups of nine is the same as nine groups of three.

We can remove one group of three, there we are.

The equation still looks the same.

So 10 groups of three subtract a group of three is equal to nine groups of three.

I know that 10 times three is 30 and now I just need to subtract three.

30 subtract three equals 27.

So nine times three is equal to 27.

Over to you.

I can see an array here.

So what I'd like you to do is change the array to show nine groups of five.

Think about what you are starting with first and then how you're going to change that.

You can pause the video here.

Off you go, good luck.

Well, nine groups of five is one group of five less than 10 groups of five.

You can use facts from the 10 times tables to help you calculate your nine times tables.

Now Jacob wants to calculate six groups of nine or six times nine.

Remember Jacob, we can use a different fact.

We know that six times 10 is equal to 60.

I'm going to visualise an array.

I can imagine 10 rows of six, which is six times 10.

Now it doesn't matter which way you visualise it.

It might be portrait in your mind, it might be landscape as long as you're visualising six groups of 10.

Now if you want to calculate six groups of nine, what do you need to change? Well, that's nine rows of six.

So it's six less than? Six times 10.

Yes, and we can record this as six times 10.

Six groups of 10 subtract six which is equal to six groups of nine.

So that means 60 subtract six is equal to 54.

So six times nine is equal to 54.

Over to you.

What facts can you use to calculate nine times eight? Who is correct? So Jacob says we can use 10 groups of eight subtract eight is equal to nine times eight.

And then Sofia says we can use 10 times eight subtract nine is equal to nine times eight.

You can pause the video here and click Play when you're ready to rejoin us.

So how did you do? Well, Jacob is correct because if we know, we are trying to calculate what nine times eight is, but we can use our 10 times table.

So in this case the table fact 10 times eight and then subtract a group of eight to calculate what nine times eight is.

So what is that? So 80 takeaway eight leaves us with 72.

I know that 60 times 10 is equal to 600.

Can you use that to calculate 60 times nine? Well, there are 10 groups of 60 which makes 600.

I want to find nine groups of 60.

I can subtract one group of 60 from 600.

600 subtract 60 is equal to 540.

I can show what you did as an equation.

So we've got here 60 groups of 10 subtract 60 is equal to 60 groups of nine.

Let's move on to our task for this lesson cycle.

So for question one, you're going to complete the examples.

If four times 10 is equal to 40, then three times nine is equal to? Subtract one group of? Four times 10 subtract? Is equal to four times nine.

And four times nine is equal to? And for question B.

If 10 times six equals 60, then nine times six is equal to something subtract one group of? 10 times six subtract? Is equal to nine times six.

Nine times six is equal to? Okay, and for question two, you're going to complete the examples.

For 2a, if 17 times 10 is equal to? Then 17 times 10 subtract? Is equal to 17 times nine.

17 times nine is equal to? And for 2b, if 10 times 47 is equal to? Then 10 times 47 subtract something is equal to nine times 47 and nine times 47 is equal to? So you're finding the missing product there.

You could pause the video here and click Play when you're ready to rejoin us.

Off you go, good luck.

So how did you do? Well for question one, this is what you should have got.

If four times 10 is equal to 40, then four times nine is equal to 36, and that's because you are subtracting one group of four.

Now if 10 times six is equal to 60, then nine times six is equal to 54, and that's because you're subtracting one group of six.

Now if 17 times 10 is equal to 170, then 17 groups of nine is equal to 153 because you're subtracting one group of 17.

And lastly, if 10 times 47 is equal to 470, the nine times 47 is equal to 423 because you are subtracting 47.

Well done if you manage to get all of those questions correct.

So now we're going to move on to solving problems. Now the 10 times table and multiples of 10 can be used to calculate other problems that involve multiplying by nine.

Sofia's mom enjoys a coffee from her favourite cafe.

In one month, she buys nine coffees.

Each coffee cost three pounds.

How much does Sofia's mom spend on coffee? So we can see that Sofia's written an equation for this.

Nine times three pounds is equal to? Now she says she doesn't know that table fact yet, but she does know what 10 times three is.

So in this case, 10 times three pounds is equal to 30 pounds.

So if she bought 10 coffees, that would be 30 pounds.

But she only bought nine coffees, so she needs to subtract three pounds.

30 pounds subtract three pounds is equal to 27 pounds.

So that means mom spent 27 pounds on the coffees.

Now Jacob says he did this using a different way, using a different fact that he knows.

He knows that two times nine is equal to 18.

So if each coffee costs two pounds, then it would cost 18 pounds.

But each coffee costs one pound more than that.

So I need to add nine pounds, 18 pounds add nine pounds equals 27 pounds.

So which method do you prefer and why? I really like Sofia's method more because I like the fact that we're only having to subtract one group of three pounds at the end.

It just makes it easier for me to calculate.

Now let's move on.

Balloons come in packets of nine.

Jacob's granddad buys 18 packets ready for a party.

How many balloons does he have? The calculation I need to do is 18 times nine.

Don't know that.

18 times 10 is equal to 180.

I can use this to help me.

This is too many because the packets have nine inside, not 10.

I need 18 fewer balloons.

So in other words, 18 groups of 10, subtract 18 is equal to 18 times nine.

180 subtract 18 is equal to 162.

So 18 times nine is equal to 162.

"My granddad has 162 balloons.

My party will look great." Over to you.

Miss Green, Jacob's teacher, buys nine packets of crayons for the classroom.

There are 16 crayons in each packet.

How many crayons are there? So what calculation do you need and what other calculation can help? You could pause the video here and click Play when you're ready to rejoin us.

So what did you get? Well, we're calculating what nine times 16 is equal to.

We know that 10 groups of 16 subtract one group of 16 is equal to nine groups of 16, 10 times 16 is equal to 160.

So nine times 16 is equal to 144.

There are 144 crayons altogether.

Onto the main task for your lesson cycle.

So for question one, you're going to use a known multiple of the tens calculation to solve these problems. 1a, Andeep has five flowers with 10 petals.

He has 50 petals altogether.

If Izzy has five flowers with nine petals, how many petal does she have altogether? 1b, packets of panda stickers cost nine pounds each.

How many does Sofia spend on seven packets? 1c, cupcakes come in boxes of nine.

For a class party, Mrs. Hopper buys 14 boxes.

How many cupcakes does she have for the party? And 1d, paintbrushes come in packets of 25 and there are nine packets of paintbrushes in the Art room.

How many paintbrushes are there in the Art room? 1e, Jacob commits to reading nine pages of his book every day for the month of January.

His book is 300 pages long.

Will he have finished the book by the end of January? And question two, complete the equation and write your own problem when nine is one of the factors.

So you've got 15 multiplied by 10 subtract something is equal to 15, multiply by? You can pause the video here.

Off you go, good luck.

So how did you do? Well for question one, you should have got 45 petals and that's because five groups of 10 subtract one group of five is equal to five groups of nine, which is 45.

For question B, you should have got 63 pounds or 63 as your product because seven groups of 10 subtract one group of seven is equal to seven groups of nine.

For question C, you should have got 126 cupcakes.

And that's because 14 groups of 10 subtract one group of 14 is equal to 14 groups of nine, and 14 groups of nine is equal to 126.

For question D, you should have got 225 paintbrushes.

And that's because 25 groups of 10 subtract one group of 25 is equal to 25 groups of nine.

So the product is 225.

For question E, Jacob would've read 279 pages.

So we know that in January there are 31 days.

So that's one of our factors.

Now if we know what 10 groups of 31 is, we can use that table fact.

So 10 groups of 31 subtract one group of 31 is equal to nine groups of 31.

So our product is 279.

For question two, this is what you could have had.

So for example, if one of the factors is nine, we could have had 15 times nine as our final equation there.

And because there is one less group of nine, it means we're subtracting 15.

And a word problem that you could have had is, "A baker makes 15 trays of cookies each with nine cookies on, how many cookies did she make?" So as long as your factors were 15 and nine in that word problem, you are correct.

Well done, we've made it to the end of the lesson.

I'm super proud of you.

Let's summarise our learning.

So today you used your known facts from the 10 times tables to solve problems involving the nine times tables.

You should now understand and know that, the 10 times tables facts can be used to find the nine times table facts.

Multiples of 10 can be used to find multiples of nine by adjusting the product.

This can be represented by an equation.

So for example, 15 times 10 or 15 groups of 10, subtract one group of 15 is equal to 15 groups of nine.

I hope you really enjoy this lesson and that you learn quite a bit.

Using facts from our 10 times tables is super helpful, especially when we don't know the products or multiples and questions to do with the nine times tables.

So in the, if you do come across a question where you have to find the answer to a question that involves your nine times tables, do think about your 10 times tables.

Thank you for joining me and I look forward to seeing you in the next one, bye.