Lesson video

- Hello everyone.

I'm Miss Brinkworth, I'm going to be going through this math lesson with you today.

If we look at our learning objective, what we're doing today is we're learning to solve addition and subtraction word problems with unknown values.

What we're talking about here is these word problems that are slightly trickier.

They might be slightly wordier.

They might have, they might not be completely clear straight away what operation is needed or what the question is actually asking us.

So I'm really hoping that by the end of today's lesson, you'll feel confident to answer a range of word problems about addition and subtraction.

So let's look at today's lesson agenda.

So we're going to start with those mental strategies.

It's a really good idea just to get us thinking about addition and subtraction really clearly, and we always need to use those mental strategies.

Even when we have got a written method to help us.

We're then going to look at how bar models can help us, especially with these trickier word problems. We're then going to think about what is the best method to answer each question.

A written method might not always be the most appropriate strategy and what is the best strategy for me? What I prefer might not be what you prefer.

As long as we're getting to an answer accurately, then that strategy is absolutely fine.

We will then have time for you to practise your new skills in your independent work and have a go at the exit quiz to see how well you've got on with today's learning.

So all you'll need is a pen or pencil, and something to write on, some paper.

A positive attitude's going to really help you because you're going to feel great about word problems by the end of the lesson.

So take your time to get what you need.

Wonderful.

Let's get started then.

Here's your first warmup of the lesson.

Here's our facts, 234 add 7 is 241.

Use that fact to fill in the unknowns on these other addition and subtraction questions.

Let's see how you got on.

So something add something equals 241.

Well, we've got those two values there haven't we? So we can swap them around, 7 add 234 is 241.

Then we've got two subtraction questions.

So 241 take away something equals 234, well, we're only going to take away a small number because we're still ending up with 200 and something so we'll use that as the number that's missing there, that goes there.

And then the subtraction that can go in the other direction, 241 take away 234 gives us 7.

So this is a nice reminder that math is often about using our known facts in new situations.

Maths isn't about learning something new all the time, but it's applying that to new questions and that's exactly what word problems ask of us.

So this is what we're going to be practising today with our word problems. Okay, warm up number two, here's a question for you.

These sums have been created, these calculations, sorry, have been answered.

One of them has been answered incorrectly.

Can you spot which one has been answered incorrectly and even better, can you spot the mistake and maybe even why someone might've made that mistake? Well done, everybody.

Well, hopefully you could see, it was the addition question here where there's a mistake and the mistake comes straight away.

So if you check this question, just like you would answer it by starting in the ones column, you can spot that mistake straight away, I hope.

Nine add 1 is 10.

So we shouldn't have a 1 in the ones column.

We should have 0 and that 1 should move into the tens column.

So I think maybe they've got a little bit confused about which number goes where when you need to regroup into the next column.

So here's the correct answer.

Really, really well done if you were able to see that, everybody.

The subtraction, the column subtraction done there is done really well, it's actually done perfectly.

So nothing, nothing wrong with that.

Okay.

Here's the type of word problem we are looking at.

And sometimes you can just look at a word problem and think, oh, there's so much writing.

It's really easy to get lost in it, to get bogged down and to get muddled.

So let's go through it together clearly, and we'll see what this question is asking of us.

I really find it helps to actually read the question out loud.

We might feel a bit silly, but it really does help.

So let's go through it.

For most of the year, Edinburgh has 356 official tourist sites.

Wow, what an amazing place.

Edinburgh must be packed full of interesting things to see.

356 tourist sites, I'm imagining this bustling city with something interesting to see on every street.

This increases greatly during the Edinburgh festival in August when a total of 737 are listed.

Oh, okay, so it increases.

Edinburgh gets even more interesting sites so that in August there are a total of 737.

How many more tourist sites does the festival create? Okay, well, let me think about this question carefully.

We've got Edinburgh, this really interesting place with loads of tourist sites, then something happens in August.

They have this festival, they get even more tourist sites.

So that in August there are 737 in total.

So that includes the ones that there normally are and the ones that are created by the festival.

So that's our total, isn't it? 737 is our total, our whole.

So we've got our whole and we've got one part, there's our 737 that are there during the festival.

We've got our 356 that are there the rest of the time.

And there we can see our unknown is a part, we're looking for a part of the whole.

Hopefully you can see that if we're looking for a part of the whole, the question is a subtraction question.

We've got the whole, we need to subtract the part to find the other part.

If we subtract how many tourist sites there normally are in Edinburgh, from the amount that they have during the festival, what we'll be left with is the number that the festival creates.

And we'll answer that question for it.

So this is a subtraction question and there it is written out.

737 take away 356.

I've still got my bar model there to help me.

Now, what I like to do is to estimate before answering a question, especially if it's a slightly trickier one like this, so I'm going to round each of the numbers and then I'm going to just subtract them quickly in my head, just to give me an idea of the answer that I'm looking for.

So here's my estimate, 740 take away 360 is 380.

So that just gives me an idea of the answer that I'm looking for.

You don't have to do an estimate, but I do find it's useful.

You don't have to write it down, you can just keep it in your head if you need to, but it does help you check your answer at the end.

Okay, here's my question.

And I've chosen to do some column subtraction.

This is because I know that I'm going to have to do some regrouping.

If I look at my tens column, I can see that I've got 5 bigger than 3, so I need to regroup in my tens column.

So firstly, starting with my 1, 7 take away 6 is 1.

And then in my tens, I can't, it doesn't seem like I've got enough tens to do 3 take away 5.

So I'm going to exchange from my hundreds.

7 becomes 6 in my hundreds column.

3 becomes 10.

Okay, 13 take away 5.

Well, I'm going to split 5 up into 3 and 2.

I can take my 3 away first to get me to 10 and then take 2 more away, gets me to 8 and then I just need to make sure I'm careful when I subtract my hundreds, that I am subtracting from 6, not from 7.

So 6 take away 3 is 3.

And there's my question answered.

So I read the question really carefully, out loud.

It can help.

I get a picture in my head of what the question is asking me.

I have a go at creating a bar model to see if I'm looking for the whole, or if I'm looking for a part, what are my knowns and what my unknowns.

I then have a go at rounding for an estimate.

I then choose the method that I'm going to use to answer the question, in this case column subtraction, and then I answer the question carefully by that method, including any exchanging or regrouping that I need to do.

Finally, I can check my answer against my estimate.

How did I do? Well, my estimate was 380, and my final answer was 381.

So I can see that I'm on the right track here with that answer.

Let's have a go at another one.

Elly sorted all the photos from her trip to Edinburgh into two separate folders.

Okay, so she had a wonderful holiday and she's taken lots of photos.

I am imagining how with old fashioned photos, ones that you actually hold like pieces of paper and she's putting them into two separate piles.

You might want to imagine her actually on a computer, moving them from computer file to computer file.

Either way, she's got two folders.

In the people folder she has 157.

And in the sights folder she has 294.

How many photos did she take? Right.

Well, they're both photos, she's got two parts.

We need to put them together to find the whole.

So my bar model there, I can see I've got my two parts.

That's my known, and I'm looking for a whole.

If I'm going to get two parts and put them together to find a whole, hopefully you can see that that's going to be an addition question, to add those two parts together.

So again, I'm going to have a go at an estimate.

I'm going to round each number.

So I've got 160, I have 290, so I'm looking for a figure around 450.

Again, I've gone for the column method.

This is because I know I'm going to have to regroup I can see just by looking at my ones.

7 add 4 is going to give me a number bigger than 10.

So I've set that out nicely into my columns and now I can go through answering the question.

7 add 4, or 7 add 3 is 10.

So 7 add 4 must be 11.

I get 1 in my ones column and 1 comes under my tens there.

5 add 9, 5 add 10 would be 15, so 5 add 9 must be 14.

But then I do have that extra one to add on from my one's column, so I've got 15 there.

1 moves over into my hundreds and then, don't forget to add your hundreds accurately.

Sometimes we're so relieved that we've done all our regrouping that we forget to just do that little bit of extra math left in our hundreds column.

1 add 2 is 3, and don't forget the one underneath that I've regrouped from my tens, gives me 4.

Again, now I can check that against my estimate.

I got 451 in my answer, and I have 450 as my estimate.

So I can see that was quite an accurate estimate.

Okay, your turn.

I'll read the question and I've given you a bar model there to help you as well.

So 256 more children visited Edinburgh Castle in March compared to February.

Maybe get in your head, why might people go in March? Maybe the flowers are starting to go up.

It's starting to be a bit warmer.

March has more people than February.

The total number of children visiting in March was 486.

How many visitors in February? Pause the video, have a go at estimates if you'd like to, and choose your method and have a go at answering that question.

Great.

So hopefully you can see from the bar model that this is a subtraction question.

You've got the whole and you've got the part and we're trying to find a part.

A part is smaller.

If we're going to get a number which is smaller than the number we started with, it must be a subtraction question.

So our subtraction question is 486 take away 256.

I've done an estimate here.

Well done if you did one as well, just a quick rounding, and that's quite a nice, easy estimate to work out.

I'm looking for a number around 240, and then here is the question.

Now you might have decided not to do a column, written strategy.

You might have decided that you could answer this question in your head.

There's actually no regrouping or exchanging needed.

So you might decided to do this one in your head, really well done if you did.

If you didn't, don't worry, I probably would have still done a written method as well, to be honest, because then I can be really sure that I've checked each column carefully.

So 6 take away 6 is 0, 8 take away 5 is 3, and 4 take away 2 is 2.

And there we can see my estimate, 230 quite close, sorry my estimate was 240, quite close to my correct answer of 230.

Okay, so here's my way of answering word problems. These are some things that I find really help me especially when a word problem is a little bit trickier.

So I like to create a bar model to show what is known and what is unknown, what information have I been given? And what is the question asking for me to find in the answer.

Sometimes, or quite often, I like to round and find an estimate so I can check that my answer's in the right place.

Complete using the best method.

This might not always be a written method.

It's up to you to decide which method you'd like to use, and then check your answer carefully against your estimate, if you've made one, or just check that the answer looks reasonable.

Remember that addition questions will get bigger and subtraction questions, the answer will be smaller.

So it's really useful to just look at your answer quickly and just think, does that look like a reasonable answer looking at the question.

Okay.

Time for your independent task.

Pause the video and take as long as you need to answer these word problems. Okay, let's see how you got on.

I'm just going to Whichever method you used to get to the correct answer is absolutely fine.

I would probably have used column addition or subtraction for each of these, but that doesn't mean that's the right strategy for you.

As long as you're getting the answer right, the strategy is fine.

So for this question, Josh played two rounds of laserblast, but couldn't remember his score in the first round.

He scores 425 in the second round and 867 in total.

What was his first round score? Well, this is a subtraction question.

We've got the total, we've got one part.

We're looking for another part.

So well done if you saw it was a subtraction question and even more well done if you got that accurate answer, 442.

Mo and Kelsey are playing Monopoly and Mo landed on one of Kelsey's hotels.

He had to pay her 450 pounds, which meant he only had 263 left.

How much did Mo have before he landed on the hotel? Well, we know how much he's got left.

We know how much it cost him to land on the hotel.

We've got two parts, together that must be how much money he had before he landed on the hotel.

We've got our two parts, we're looking for a whole.

Well done if you saw this was an addition question.

And even more well done if you got the correct answer.

713.

Really I should have a pound sign there.

713 pounds is the answer to that question.

Okay, question three.

There were 200 fewer fireworks accidents in Leicestershire this year compared to last year.

If there were 497 this year, how many accidents were there last year? So this is where it's really important to read what it's telling us carefully.

We've been given the figure for this year, and the question tells us that there were less this year, there were 200 more last year.

So we've got our two parts.

We're looking for the whole, this is an addition question.

And even better if you saw that, actually you probably didn't need a written method to answer this question as you're just adding 200, you just need to change the hundreds column.

Well done if you got that answer right.

Okay, decide which of these bars is a subtraction and which is an addition question.

These can be used interchangeably a little, but actually when we look at our bar model where we've already got the whole and we're looking for a part, that is normally a subtraction question and addition where we've got both parts and we're looking for a whole.

Obviously we could have more than two parts.

We might need to add three or four numbers together to find the whole.

It would still be an addition question.

Okay, and this final question, can you se a mistake that I've made? So it says that Beka mixed 275 ml of red paint with a tin of white paint to make 633 ml of pink paint.

And the question should be how much, what's the missing value? So how much was in that can of white paint? Hopefully you can see that it's not adding these amounts together.

You've already been given the total.

My bar model suggests I'm looking for the total.

I'm not, I've been given the total.

She made 633 ml of pink paint.

So my bar model needs to change slightly to show that what I'm looking for is a part and really, really well done if you could see that.

And there's the question and the answer.

Okay, now it's time for you to complete the quiz and see how well today's learnings gone in.

I'm really impressed.

There's a lot of really tricky things you needed to see there.

You could see from our success criteria there were lots of different steps.

And if you've managed to get on well with a few of them, I'm very, very pleased with you.

Enjoy the rest of your day, everybody.