Lesson video

Hello, my name's Mrs. Hopper, and I'm really looking forward to working with you in today's math lesson.

It's from our unit adding and subtracting ones and 10s to and from two-digit numbers.

So we're going to be looking at two-digit numbers and we're going to be thinking about adding and subtracting and hopefully using our known facts to help us.

So if you're ready, let's make a start.

So in this lesson, we're going to be finding 10 more and 10 less than a two-digit number.

We've got lots of keywords today.

We've got 10 more, 10 less, increase and decrease.

So I'll take my turn to say them and then it'll be your turn.

So my turn, 10 more.

Your turn.

My turn, 10 less.

Your turn.

My turn, increase.

Your turn.

My turn, decrease.

Your turn.

Well done.

I expect there are words in there that you know already.

They're going to be really useful to us, so look out for them as we go through today's lesson.

There are two parts to our lesson.

In the first part, we're going to be finding 10 more and 10 less in the counting sequence.

And then in the second part, we're going to be looking at 10 more and 10 less with resources.

So if you're ready, let's make a start on part one.

And we've got Alex and Sam helping us with our learning today.

The children are using a Gattegno chart to count forwards and backwards in multiples of 10.

Let's help them.

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

Let's count backwards starting with 100.

Are you ready? 100, 90, 80, 70, 60, 50, 40, 30, 20, 10.

We can see the pattern more clearly when we dual count.

So let's count in groups of 10.

One 10, two 10s, three 10s, four 10s, five 10s, six 10s, seven 10s, eight 10s, nine 10s, 10 10s.

And let's count backwards from 10 10s.

10 10s, nine 10s, eight 10s, seven 10s, six 10s, five 10s, four 10s, three 10s, two 10s, one 10.

Alex says, "What do you notice about the digits in each number?" And Sam says, "The 10s-digit changes, but the ones digit remains the same." We're counting in multiples of 10, we're adding and subtracting 10 each time.

When we count in 10s, the 10s-digit changes, we can use this to help us find 10 more than a multiple of 10.

So let's start counting.

10, 20, 30, 40, 50.

Oh, Alex says, "What is 10 more than 50?" And Sam says, "Six 10s has one more 10 than five 10s.

We know 50 is five 10s." So 60 is 10 more than 50.

It's one more 10.

There it is, 60.

When we look at these numbers, what's the same and what's different? Sam says, "The 10s digit has increased by one, but the ones digit remained the same." We've got no extra ones in our multiples of 10.

We can also use this to help us find 10 less than a multiple of 10.

So what's 10 less than 50, Sam asks? And Alex says, "Four 10s has one less, 10 than five 10s.

So 40 is 10 less than 50." 50 has five 10s and 40 has four 10s.

"The 10s digit has decreased by one, but the ones digit remain the same." The children explore this pattern on a 100 square.

Can you see the multiples of 10? Let's help them.

Let's count from 10.

Are you ready? 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.

And backwards from 100.

Are you ready? 100, 90, 80, 70, 60, 50, 40, 30, 20, 10.

Great counting.

And again, we can see that pattern more clearly when we dual count.

Remember, we can count in one 10s, two 10s, three 10s, so let's try that.

One 10, two 10s, three 10s, four 10s, five 10s, six 10s, seven 10s, eight 10s, nine 10s, 10 10s.

And let's count backwards.

10 10s, nine 10s, eight 10s, seven 10s, six 10s, five 10s, four 10s, three 10s, two 10s, one 10.

"What do you notice?" Says Alex.

I wonder what you do notice.

When we count forwards in 10s, the 10s digit increases by one, but the ones digit remains the same.

And when we count backwards in 10s, the 10s digit decreases by one, but the ones digit remains the same.

Sam picks a number, she wants to count on by adding 10 more each time.

"I wonder how we can find 10 more than a number that is not a multiple of 10." Ooh, that's interesting, Sam.

When we find 10 more, the 10s digit changes, but the ones digit stays the same.

Let's dual count to help us see the pattern.

So she's chosen one 10 and four.

So one 10 four.

So we're gonna add 10 each time.

one 10 four, two 10s four, three 10s four, four 10s four, five 10s four, six 10s four, seven 10s four, eight 10s four, nine 10s four.

The 10s digit increases by one, but the ones digit remains the same.

Let's use this to help us count on in 10s.

So we know that one 10 and four is 14.

So let's count on in 10s each time.

14, 24, 34, 44, 54, 64, 74, 84, 94.

And we can use this to find 10 more, says Sam.

Let's look at 54 then.

One more 10 is 60, 64.

"So 10 more than five 10s and four is six 10s and four.

So 10 more than 54 is 64." Sam picks a number, she wants to count back in 10s this time.

Oh, she started with nine 10s and nine, 99.

When we count back in 10s, the 10s digit will change, but the ones digit will remain the same 'cause we're just taking away one 10 each time.

So we've got nine 10s nine, eight 10s nine, seven 10s nine, six 10s nine, five 10s nine, four 10s nine, three 10s nine, two 10s nine, one 10 nine.

So each time we had one fewer 10.

Now, let's count in a different way.

We know that nine 10s nine is 99.

So let's count back in 10s from 99.

Are you ready? 99, 89, 79, 69, 59, 49, 39, 29, 19.

And we can use this pattern, Sam says to help us find 10 less than 49.

So we can see 49 in our count and 49 on the Gattegno chart.

So 10 less will be one 10 fewer.

So we know that three 10s and nine is 10 less than four 10s and nine.

So we know that 39 is 10 less than 49.

There it is on the Gattegno chart and in our count.

Alex uses the pattern to find 10 more and 10 less on 100 square.

10 more than five 10s seven is.

well, let's help him to complete the stem sentences.

He says, "I know that when I find 10 more, the 10s digit will increase by one, but the ones digit will stay the same." So we started with five 10s and 7, 57.

There it is on our 100 square, five 10s and seven ones, five 10s seven.

So 10 more would be six 10s and seven ones.

So 10 more than 57 is 67.

And we can also help him to complete the stem sentences when we're thinking about 10 less.

And Alex says, "I know that when I find 10 less, the 10s digit will decrease by one and the ones digit will stay the same." So we're still on 57, five 10s seven.

This time our 10s digit is decreasing by one.

So 10 less than five 10s seven is four 10s 7.

10 less than 57 is 47.

Time to check your understanding.

Let's use the pattern on the 100 square to complete the stem sentences.

So we've got our starting number of 63, six 10s three, and you are going to complete the sentences to find 10 more and 10 less.

So pause the video, have a go, and when you're ready, we'll get together for some feedback.

How did you get on? So 10 more than six 10s three is seven 10s three.

And we know that six 10s three is 63, so 10 more than 63 is 73, and we can see it there on the 100 square.

So what about 10 less? Well, 10 less than six 10s three is five 10s three.

So 10 less than 63 is 53.

Well done, if you've got those right.

So the children use the pattern in the 10s digits to find the missing numbers on the number line.

So can you see, we've got a number line marked in multiples of 10, but then we've got some numbers marked on the top of the line and all of them have got six ones.

And Alex says, "When we find 10 more, the 10s digit increases by one, but the ones digit remains the same." He says, "26 is two 10s six.

So 10 more is three 10s six, or 36." So he reckons that first missing number will be 36.

There it is.

Sam says, "I worked it out a different way." She says, "We know that when we find 10 less, the 10s digit decreases by one, but the ones digit remains the same.

So 46 is four 10s six, so 10 less is three, 10s six, or 36." So she worked it out by thinking about 10 less than 46.

"Now let's find the other missing number," says Alex.

66 is six 10s six.

So 10 more is seven 10s 6, or 76.

Sam says, "Or you could say that 86 is eight 10s six.

So 10 less is seven 10s six, or 76." Let's use the pattern in the 10s digits to complete the number tracks.

So we've got 27, 37, 47 to begin with.

Sam says, "The 10s digit is increasing by one, but the ones digits stays the same." So our pattern would continue 57, 67, 77, 87, 97.

And you might have thought two 10s seven, three 10s seven, four 10s seven and so on.

What about the next one? We've got 98, 88, 78, 68.

What do you notice there? Ah, Sam says, "The 10s digit is decreasing by one, but the ones digit stays the same." So the pattern will continue 58, 48, 38, 28.

What about the last one? We've got gaps sort of in the middle here.

Well, Sam says, "10 more than 51 is 61, and 10 less than 91 is 81." So she filled one in thinking about 10 more and the other one thinking about 10 less.

I wonder how you did it.

Time for you to have some practise now.

In question one, you are going to fill in the missing numbers, thinking about 10 more and 10 less than the number given.

And first, the second part, you are going to think of all the different ways that you could complete the following correctly.

Try and find all the possible solutions.

So in A, you've got missing 10s and four ones in both.

And in B, you've got seven 10s and eight 10s, but no ones digits.

So pause the video, have a go at your tasks, and when you're ready, we'll get together for some feedback.

How did you get on? So for one A, we had 65 and we had to work out what was 10 more.

10 more than 65 is 75 or 10s digit has increased by one, our ones digit has stayed the same.

For B, we already knew that the 10 more was 66, so we were trying to find 10 less.

And that was 56, our 10s digit has decreased by one, our ones digit has stayed the same.

And then we had 66 in C and we had to find 10 more.

So we've got six 10s in 66.

So we need seven 10s in 76, 10 more.

What about number two? So for the first one, we just had to show that the number on the left was 10 less than the number on the right, but they both had fours as one digits.

So you could choose any pair of numbers where the 10s digits had a difference of one.

So we've got 14 and 24, 24 and 34, 34 and 44, 44 and 54, 54 and 64, 64 and 74, 74 and 84, 84 and 94.

I wonder if you found all those possibilities.

Did you list them all in order? And what about B? Well, we had 70 something and 80 something.

So this time we could choose any one's digits as long as they were the same.

So it was only our 10s digits that were changing.

So we could have had 70 and 80, 71 and 81, 72 and 82, 73 and 83, 74 and 84, 75 and 85, 76 and 86, 77 and 87, 78 and 88 and 79 and 89.

After that, there were no more one digits we could use.

Well done if you got all those right.

And on into the second part of our lesson where we're going to be looking at this using resources.

So some uses base 10 blocks to represent two numbers.

Let's think about what's the same and what's different.

She says, "I can see both numbers have the same number of ones, but the 10s are different." We've got 54 and then our other number has 10 more and it's 64.

And we can see five 10s have increased to six 10s, but our ones have stayed the same.

So we had five 10s and four ones, 10 more gives us six 10s and four ones.

When we find 10 more, the 10s digit changes and the ones digit stays the same.

And we can see that on a place value chart, five 10s and four ones, increasing to six 10s, but the four ones staying the same.

Alex represents two different numbers with base 10 blocks.

What's the same and what's different about these two numbers? Well, Alex says, "Both numbers have the same number of ones, but the number of 10s is different." We've got 35 and then we've got 10 less, we've got 25.

We had three 10s and five ones, 10 less gives us two 10s and five ones.

And we can see that on the place value chart, three 10s and five ones, 10 less gives us two 10s and five ones, the ones remain the same.

Time to check your understanding, use the base 10 blocks to complete the stem sentences.

What do you notice about the 10s and the ones numbers in each number? Pause the video, have a go, and when you're ready, we'll get together for some feedback.

How did you get on? Did you spot that we had seven 10s and six ones to begin with and then we had 10 more to give us eight 10s and six ones? And we can represent that on the place value chart.

Seven 10s and six ones, 76.

One more 10, we have eight 10s and six ones.

We have 86.

And let's think about it the other way.

So we had eight 10s and six ones and 10 less gives us seven 10s and six ones.

And if we looked at our place value chart, eight 10s and six ones, 86, 10 less, seven 10s and six ones, 76.

The ones have stayed the same, the 10s are different.

So let's think about how the 10s change when we find 10 more.

What is 10 more than 48? To find 10 more, we add one more 10.

And Sam says, "I will draw the 10s and ones." So we had four 10s and eight ones, and now, we've got five 10s and eight ones.

And you could see the place value chart changing at the same time.

48 and 10 more will be equal to 58.

So there's our 58.

She says, "I noticed the 10s digit increase by one." We had four 10s and now we have five 10s.

Now, let's think about how the 10s change when we find 10 less.

So we've got our 48 to start with.

What is 10 less than 48? SO to find 10 less, we remove one 10.

Sam says, "I'll draw the 10s and ones." Ah, so now, she's just drawn three 10s and eight ones.

And 48 has changed to 38.

She says, "I noticed that the 10s digit decreased by one.

10 less than 48 will be 38." Time to check your understanding.

Can you draw the base 10 blocks to represent the number that is 10 more than the number and that is 10 less than the number shown? Pause the video, have a go, and when you're ready, we'll get back together for some feedback.

How did you get on? When we find 10 less than 68, the ones digit will stay the same but the 10s digit will decrease by one.

So we needed to draw five 10s and eight ones.

68 has now got only five 10s 'cause we've removed a 10, but we've still got the eight ones.

So 10 less than 68 is 58.

When we find 10 more than 68, the ones digit will stay the same, but the 10s digit will increase by one.

So we had six 10s and now we have seven 10s and eight ones.

Seven 10s and eight ones, so 78 is 10 more than 68.

Alex draws the base 10 blocks to make a number sequence and then hides some of the numbers from Sam.

Ooh, Sam's gonna have a look at these now.

Sam draws one of the missing numbers and explains how she knows she's right.

So she says, "This missing number is 59.

I know this because 59 has one more 10 and 49 and our pattern is going up in 10s.

So the 10s digit increases by one." So we've gone from four 10s to five 10s.

She says, "I also know this because 59 has one fewer 10 than 69," so she's worked backwards from 69 as well.

So there's 69 in our place value chart, one fewer 10, the 10s digit decreases by one and we can see that in the place value chart, 69 has gone down by 10 and is now 59.

Time to check your understanding.

Can you draw the missing number and explain how you know you are right? Pause the video, have a go, and then we'll come back together for some feedback.

What did you think? Did you see that we needed one more 10, We knew 79, we needed one more 10.

So we needed eight 10s and nine ones.

89 is 10 more than 79.

I know it because it has one more 10.

79 and one more 10 is 89.

So that's our missing number.

And we can also think back from 99.

89 is 10 less than 99.

And I know because it has one less 10.

99 and one less 10 is 89.

Well done if you got that right.

Sam has 65 p, and Alex has 10 p more.

How much money does Alex have? So we're thinking about our 10s, but we're thinking about 10 Ps now.

So Sam has six 10s and five ones.

To find 10 more, we increase the 10s digit by one, but the ones digit stays the same.

So 10 more gives us seven 10s, and there is our extra seven 10 and five ones.

So how much money is that? Ah, Alex says, "I have 75 P." Alex spends 10 P.

How much money does he have now? So Alex had seven 10s and five ones.

Oh, Sam says, "To find 10 less, we decrease the 10s by one.

The ones digit will stay the same." So 10 less gives us six 10s and five ones.

So Alex says, "I have 65 P," he spent his 10 p.

Time for you to do some practise.

Can you draw the base 10 blocks into the chart to show the number that is 10 less and then the number that is 10 more from the numbers in the middle? Pause the video, have a go, and when you're ready, we'll get together for some feedback.

How did you get on? So we know that when we find 10 more or 10 less, the ones digit stays the same.

The 10s digit will increase or decrease by one.

And do you notice that all our numbers have the same number of ones anyway? So 10 less than four 10s and five is three 10s and five.

So 10 less than 45 is 35.

10 more than four 10s five is five 10s five.

So 10 more than 45 is 55.

10 less than five 10s five is four 10s five.

So 10 less than 55 is 45.

10 more than five 10s five is six 10s five.

So 10 more than 55 is 65.

And finally, 10 less than six 10s five is five 10s five.

So 10 less than 65 is 55.

And 10 more than six 10s five is seven 10s five.

So 10 more than 65 is 75.

Well done if you've got all those right, lots of 10s and ones to draw there, weren't there? And we've come to the end of our lesson.

We've been finding 10 more and 10 less than a two-digit number.

So what have we learned about today? We've learned that when finding 10 more or 10 less than any two-digit number, the ones digit does not change because we're only changing the number of 10s.

When we find 10 more than a number below 100, the 10s digit increases by one.

And when we find 10 less than a number below 100, the 10s digit decreases by one.

We were only working with two-digit numbers.

So the numbers up to numbers in their 90s today, weren't we? Thank you for all your hard work and your mathematical thinking today.

I hope you've enjoyed the lesson and I hope I get to see you again soon.

Bye-bye.