Lesson video

Hello there.

My name is Mr. Goldie and welcome to today's maths lesson.

And here is our learning outcome.

"I can identify knowns and unknowns in subtraction equations." And here are keywords today.

So I'm going to say each keyword, can you repeat it back? So the first keyword is minuend.

The next keyword is subtrahend, and the next keyword is difference.

And let's take a look at what those words mean.

So the minuend is the number being subtracted from, a subtrahend is a number subtracted from another, and the difference is the result after subtracting one number from another.

So in the equation, seven, subtract three equals four.

Seven is the minuend, three is the subtrahend, and four is the difference.

And here's our lesson outline.

So in the first part of the lesson, we are going to be looking at subtraction with missing parts.

And in the second part of the lesson we are going to be looking at subtraction with a missing whole.

Let's get started.

In this lesson you'll meet Lucas and Izzy and they're going to be helping you with your maths today.

"Snails are my favourite animals." says Izzy.

That might give you a clue as to what animal might be appearing in this math lesson.

Lucas and Izzy are measuring how fast snails travel in one minute.

We put each snail 100 centimetres away from a leaf.

100 centimetres is of course the same as one metre.

We measured how far each snail correct in one minute.

So snails are famous of course, for being quite slow moving creatures.

Some of these snails are slower than others.

They start with Shelby.

Here's Shelby.

Shelby travelled 40 centimetres in a minute.

I'm going to work out how much further Shelby has to travel to reach the leaf.

Izzy uses a bar model to represent the problem.

So we've got minuend being the hole and subtrahend and difference being the parts.

100 centimetres is the whole, and 40 centimetres is one of the parts.

That's how far Shelby travelled.

Izzy wants to find out this part.

Izzy needs to subtract the subtrahend from the minuend.

100 centimetres subtract 40 centimetres equals 60 centimetres.

So 60 centimetres is the missing part.

Shelby still has to travel 60 centimetres.

They test out Suzie next.

And here's Suzie.

Suzie's moved quite a long way, hasn't she? Suzie is 20 centimetres away from the leaf.

But how far did Suzie travel? "Oh no! I forgot to measure that." says Lucas.

It's not a problem, Lucas.

We can work it out." says Izzy.

Izzy uses a bar model to represent the problem.

So remember, minuend is the whole and subtrahend and different are the two parts.

The 100 centimetres is the whole.

This is one of the parts that's 20 centimetres.

That's how far Suzie was away from the leaf when the minute ended.

Izzy wants to find out how far Suzie had travelled.

To find a missing part, I subtract the other part from the whole.

700 centimetres subtract something equals 20 centimetres.

"I can swap around the subtrahend and the difference." says Izzy.

Izzy can swap the equation around and make it 100 centimetres, subtract 20 centimetres.

That will give her the missing part and the answer is 80 centimetres.

Suzie travelled 80 centimetres in one minute.

To find the missing part, subtract the other part from the whole.

How far has Sheldon travelled? Here's Sheldon got 100 centimetres to get to the leaf.

So after one minute, Sheldon is 30 centimetres away from the leaf.

How far has Sheldon travelled? 100 centimetres subtract what number equals 30 centimetres.

I'm going to swap around the subtrahend of the difference.

Lucas has changed the equation around and made it 100 centimetres subtract 30 centimetres equals what is 100 subtract 30? The answer is 70, 70 centimetres.

So Sheldon has travelled 70 centimetres altogether.

Work out how far Sydney has travelled here.

Here is Sydney.

After one minute, Sydney is five centimetres away from the leaf.

From 100 centimetres subtract what number equals five centimetres.

How will you find the missing subtrahend? Pause the video and see if you can work out the answer.

And welcome back.

And let's take a look at that answer.

So Luca says, "Swap around the subtrahend and the difference." So we could change the equation around and make it 100 centimetres subtract five centimetres.

That's quite easy to work out, isn't it? The missing number is 95 centimetres.

So 100 centimetres subtract 95 centimetres equals five centimetres.

So Sydney had travelled 95 centimetres.

Very well done if you got the right answer.

Shelly travels towards the leaf, which is 200 centimetres away.

So here's Shelly.

After two minutes, Shelly is 50 centimetres away from the leaf.

How far has Shelly travelled? 200 centimetres subtract what number equals 50 centimetres? We're trying to find out the missing part.

We're trying to work out how fast Shelly travelled.

"I'm going to swap around the subtrahend and the difference." says Lucas.

Lucas rearranges the equation into 200 centimetres subtract 50 centimetres equals our missing number.

100 subtract 50 equals 50.

So 200 subtract 50 must be 150.

150 centimetres.

So 200 centimetres subtract 150 centimetres equals 50 centimetres.

So Shelly had travelled 150 centimetres.

And here's a problem for you to try on your own.

Sammy moves towards the leaf which is 200 centimetres away.

Here's Sammy and there's the leaf 200 centimetres away.

After two minutes, Sammy is 80 centimetres away from the leaf.

How far has Sammy travelled? How would you work out the answer? See if you can write the equation that you would need to solve the problem.

Pause the video and have a go at trying to solve that problem.

Welcome back.

Let's take a look at how you got on and see whether you got the right answer.

So the calculation you are trying to work out is 200, subtract something equals 80.

200 centimetres subtract a missing number equals 80 centimetres.

Now swap around the subtrahend and the difference to work out the answer more easily.

So 200 centimetres subtract 80 centimetres equals 120 centimetres.

So Sammy had travelled 120 centimetres.

Very well done if you got the right answer.

When the numbers are close together, add on to find the difference.

So here's a snail and after a minute, the snail still had 92 centimetres to travel to the leaf.

Maybe it got a bit distracted on the way.

Steve has hardly moved.

Ah Steve, the snail.

100 centimetres subtract what number equals 92 centimetres.

Okay, we're trying to work out how far Steve has actually travelled.

How would you work out the answer? I could add on from 92 centimetres to 100 centimetres to find the difference.

So those two numbers are actually quite close together.

92 is not very far away from 100.

So we could easily add on to 92 to get to 100 and that will tell us how far Steve has moved.

I know two add eight equals 10.

So 92 add eight equals 100.

92 centimetres add eight centimetres equals 100 centimetres, 100 centimetres subtract eight centimetres equals 92 centimetres.

So when the numbers are closed together, add on to find the difference.

Here's one to try on your own.

How far has Sunita travelled? Now Sunita has got 200 centimetres to go to reach the leaf.

How far Sunita travelled? Sunita still has 196 centimetres to go.

Sunita is even slower than Steve.

How would you work out the answer? How would you work out how far Sunita has travelled so far? Pause the video and see if you can find the answer.

And welcome back.

Did you manage to find out how far Sunita moved? Let's have a look to see if you are right.

So the calculation you may have written down is 200 centimetres, subtract something equals 196.

We're looking for that missing number.

And remember when the numbers are close together, add on to find the difference.

You could do the calculation 200 subtract 196, but it's easier to add on to find the difference.

So 196 add what number equals 200.

196 centimetres add four centimetres equals 200 centimetres.

200 centimetres subtract four centimetres equals 196 centimetres.

Very well done if you got out how fast the metre have travelled.

And let's look at task A.

So work out how far the snails have travelled.

So you've got, there are diagram showing how far the snails have travelled and you've got, there are a couple of equations, you've gotta work out the missing parts.

Here's part two of task A.

So work out how far the snails have travelled and write the equations.

So you've gotta work out what the calculations would be and pop those in the box underneath and use those to help you work out the answer.

And here's part three.

Solve these problems. You can draw diagrams to help you.

So if you want to draw pictures to help you work out the answers, that is absolutely fine.

So problem A.

Saskia travels towards the leaf which is 200 centimetres away.

After two minutes, Saskia is 105 centimetres away from the leaf.

How far has Saskia travelled? So you got three problems there to solve as well.

So pause the video and have a go at task A And welcome back.

Let's take a look at those answers, see whether you got them right.

So here the answers for part one of task A.

So that first snail, snail A had travelled 50 centimetres so far.

So I dunno if you worked out the answer.

Here are the answers for number two.

So remember to work out a missing part.

Subtract the other part from the whole.

Well I dunno if you managed to find the answers to part two and here are the answers to part three.

So our first problem is Saskia travels towards the leaf which is 200 centimetres away.

After two minutes Saskia is 105 centimetres away from the leaf.

How far has Saskia travelled? So here's a diagram showing Saskia and the leaf 200 centimetres away and after two minutes, Saskia is 105 centimetres away from the leaf.

They could draw a bar model to help you work out the onsets.

You've got 200 there being the whole and 105 being one of the parts.

The calculation to work out the whole would be 200 centimetres subtract 105 centimetres equals 95 centimetres.

200 centimetres subtract 95 centimetres equals 105 centimetres.

Here the answers for B.

How far as Simon travelled? So after three minutes, Simon is 189 centimetres away from the leaf.

How far Simon travelled? So Simon didn't travel very far at all in three minutes because the numbers are close together, you can add on to find the difference.

So 189 centimetres add 11 centimetres equals 200 centimetres.

And here's problem C.

So after three minutes, Shen is 25 centimetres away from the leaf.

How far has Shen travelled? So how would you work out how far she's travelled? Subtract one part from the whole.

So 300 subtract 25 equals 275.

So Shen has travelled 275 centimetres.

Very well done if you've got the same to part three of task A and very well done for working out those missing parts.

And let's move on to part two of the lesson.

Subtraction with a missing whole.

Izzy is watching some snails on a log.

I've been watching them for ages.

I counted nine snails creeping away.

There are still seven snails on the log.

How would Izzy and Lucas find out how many snails were on the log to start with.

Izzy and Lucas try to work out the answer.

"I counted nine creeping away." says Izzy.

Here's a bar model and one of the parts is nine.

"There are seven snails still on the log." says Lucas.

So one of the parts is seven.

The whole is missing.

How many snails were on the log at the start? How would you work out the missing whole? The minuend is missing.

The whole can be the minuend.

A number subtract nine equals seven.

The whole subtract one part equals the other part.

"To work out a missing whole, add the parts together." says Lucas.

So to work out the number of snails on the log to start off with, you could add the parts together, nine, add seven.

Izzy thinks about how to add those two numbers together so I can partition seven into one and six.

Nine add one, add six equals 16.

So Izzy's using her number pairs, the total 10, isn't she? To help her work out the answer.

So the answer is 16.

16, subtract nine equals seven.

Izzy gives Shelby some leaves.

How many leaves was Shelby given? Shelby has eaten seven leaves and there are eight leaves left.

Again here's a bar model to represent the problem.

One of the parts is seven.

That's how many leaves Shelby has eaten and one of the parts is eight.

That's how many leaves are left.

The whole is missing.

How many leaves did Shelby start with? The calculation is something subtract seven equals eight.

The minuend subtract the subtrahend equals the difference.

To work out a missing whole, add the parts together.

Eight, add seven equals.

That's a near double, isn't it? Seven, add seven, you probably know, what's eight add seven? 15.

15 subtract seven equals eight.

So the missing number on the bar model is 15.

Here's one to try on your own.

Safi is given some leaves.

Here is Safi.

Safi has eaten 10 leaves, there are 13 leaves left.

Here's a bar model to help you solve the problem.

One of the parts is 10 and one of the parts is 13.

So Safi is eaten 10 leaves and there are 13 leaves left.

The whole is missing.

How many leaves did Safi start with? Pause the video and see if you can work out the answer.

And welcome back, how did you get on? Did you manage to work out the answer? Let's take a look and see whether you were right.

So we're trying to work out a missing whole.

Subtract a part equals the other part.

A number subtract 10 equals 13.

To work out the missing hole, add the parts together.

13, add 10.

13 add 10 is quite an easy calculation.

The answer is 23.

23 subtract 10 equals 13.

We can also compete the bar model.

Very well done if you manage to work out the correct answer.

And let's move on to task B.

Here's part one of task B.

Work out the missing number from each equation.

You can draw bar models or write an addition equation to help you.

And Lucas is just reminding you, "To work out a missing whole, add the parts together." So you may want to rewrite those sentences as addition equations.

Part two task B looks like this.

"Read each question carefully.

Think carefully about the calculation that will help you find the answer." So question A, "Shelby has eaten 12 leaves, there are 12 leaves left.

How many leaves did Shelby start with?" Think about what calculation you would use to help you work out the answer.

And here is part three of task B.

So work out the missing number from each equation.

"You can draw bar models or write another equation to help you." So these questions are testing your learning from the whole lesson today.

So Izzy is saying to find a missing part, subtract the other part from the whole.

Lucas is saying to work out a missing whole, add the parts together.

So it could be a part that's missing, it could be a whole that's missing.

So pause the video and have a go at task B.

So here are the answers for part one of task B.

So for A, the missing number was 50.

50 subtract 40 equals 10.

And remember to work out that missing whole, add the parts together.

40 add 10 equals 50.

Here are the answers for part two of task B.

Let's have a quick look at A.

So A, Shelby has eaten 12 leaves, there are 12 of leaves left.

How many leaves did Shelby start with? So we're trying to work out the missing number here.

So something subtract 12 equals 12.

To work out the missing whole, add the parts together.

12 add 12 equals 24.

24 subtract 12 equals 12.

And here are the answers for part three of task B.

So for question A, the missing number was 700 and you had to add the parts together to find that missing whole.

And for E, E was quite a tricky one.

So 30 equals 80 subtract something.

You'd have to turn that calculation around and subtract the other part from the whole.

So 80 subtract 50 equals 30.

Very well done if you've got onto part three and you've got those questions right, that's excellent work.

And hopefully you're feeling a lot more confident at trying to find missing parts and wholes when you are using subtraction.

Excellent work today.

Very, very well done indeed.

And let's move on to our summary.

So to find a missing part in a subtraction equation, subtract the other part from the whole.

So 100 subtract something equals 20.

And turn that around and subtract the other part from the whole, 100 subtract 20.

To work out a missing whole in a subtraction equations, add the parts together.

So something subtract nine equal seven, add nine and seven together to find the missing whole.