Lesson video

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This is our eighth lesson in the Decimals and Measures unit.

Today, we'll be looking at converting between standard units of mass.

All you'll need is a pencil and a piece of paper, so grab your equipment if you haven't done so already.

The agenda for today's lesson will be to begin with a quiz to test your knowledge from our previous lesson.

Then we'll look at weight versus mass.

We'll convert between grammes and kilogrammes, before solving problems involving grammes and kilogrammes.

Then you'll do some independent learning, and a final quiz.

So let's start with our initial knowledge quiz.

Pause the video now and complete the quiz and click restart once you're finished.

So let's have a look at weight versus mass.

So I want you to think about these three questions.

What do these two words mean? Can you like to definition for them? And can you explain the difference between them? Pause your video now and make some notes.

So we looked at this a little bit in one of our previous lessons.

We know that weight and mass are different.

Weight is the impact of the gravitational pull on an object.

And mass is the amount of stuff an object is made up of.

Mass and weight are often used interchangeably, but it's really important that you understand the difference between them.

So if you have a look at this example on the screen.

These bananas, they have a mass of 200 grammes.

So you can see on the scales that their mass is 200 grammes.

What this means is that they show a weight of 200 grammes on Earth.

But in space, there is no gravitational pull.

So in space, the scales, which show a weight of zero grammes, but they would still have the same mass.

They're still made up of the same amount of stuff.

So remember that they're used interchangeably, but mass is really the correct word to use when you're referring to how much stuff something is made up of.

So let's have a look now at converting between grammes and kilogrammes.

I want you to think about these two questions.

How many grammes are there in 1 kilogramme? And how could you write 1 gramme in kilogrammes? Pause the video now while you think about these questions.

So you may have used your knowledge of the prefixed kilo, which means a thousand, or you may have used the scale to count up, to figure out the equivalent of grammes and kilogrammes.

So if we know that there are 1,000 grammes in 1 kilogramme, kilo, meaning 1,000 counting up, we get to 1,000 here, then how do we convert from grammes to kilogrammes? So to get from grammes to kilogrammes, we would divide by 1,000.

And think about how we divide by 1,000.

We divide by 1,000 by moving our digits three places to the right, so that the number becomes 1,000 times smaller.

Now, if we wanted to convert from kilogrammes to grammes, we would use the inverse.

So we'll multiply by 1,000.

And then if you think about, how do we multiply by 1,000? Well, we move our digits three places to the left, so that the number becomes 1,000 times greater.

So with that in mind for today's lesson, you may want to draw yourself out a place value chart, so that you can show your multiplication and division, because today's lesson will rely heavily on your ability to multiply and divide by 1,000.

Let's look at an example together.

So we're back to our bananas.

We know that bananas have a mass of 200 grammes.

I want to know what is this in kilogrammes? So if I look at my image at the top, to convert from grammes to kilogrammes, I divide by 1,000, because 1,000 grammes is equivalent to 1 kilogramme.

And when I divide by 1,000, my number is becoming 1,000 times smaller, so my digits will move to the right, three places.

So my 2 will move three places to the right, so that it's in the 10ths column.

These zeroes are no longer needed because they're not holding a place anymore.

But I do need a place holder in my ones column, and then my decimal point.

So the mass of the bananas in kilogrammes is 0.

2 kilogrammes.

200 divided by 1,000 is equal to 0.


If you're not feeling very confident with that, perhaps change the mass of the bananas to some different numbers and have a go at moving it around in your place value chart.

But now you'll get the opportunity to practise some more.

So you have got the masses of some animals, and you need to convert them to the given units.

So pause the video while you find the mass of each animal.

If for the lion, you were given the mass in kilogrammes, and asked to convert to grammes, so from kilogrammes to grammes, you multiply by 1,000.

195 kilogrammes multiplied by 1,000 is equal to 195,000 grammes.

For the eagle owl, again, kilogrammes to grammes.

So multiplying by 1,000.


65 times 1,000 is equal to 2,650 grammes.

So for the last one, for the emperor penguin, you are converting from grammes to kilogrammes.

So dividing by 1,000.

So 24,100 divided by 1,000 is equal to 24.

1 kilogrammes.

Now let's have a look at some problem-solving involving the conversion of units of mass.

So here's our first question to do together.

A greengrocer weighs some fruit.

She removes the apples and weighs the fruit again.

The scales show the two weights, and what is the mass of the apples? So we've got the first scale shows the mass of all of the fruit, including the apples.

And the second one shows it without apples.

So if we zoom in, we can see the difference between the two here.

First of all, we need to identify what is the value of each of the scales pointing to? So with the apples, we can see that it's pointing here.

I know that each of these intervals has a value of 50 grammes because between 800 and 900 is 100 grammes and divided that in half gives us 50 grammes.

So it's actually pointing halfway between 800 and 850 grammes.

So with the apples, it's pointing to 825 grammes.

And then without them, it's pointing to halfway between 650 and 700 grammes.

So it's pointing to 675 grammes.

So I've got 825 with apples, and 675 without.

So to find the mass of the apples, I'm looking for the difference between these two amounts here.

825 subtract 675 is equal to 150 grammes, which is the mass of the apples.

Now I'd like you to pause the video and have a go at solving this problem independently.

I'll read it out to you first.

So we have three identical parcels, and two identical envelopes, that weigh 2.

1 kilogrammes all together.

If one envelope has a mass of 120 grammes, what is the mass of one parcel? My advice is to have all of your measurements in the same unit.

So perhaps convert this one first, the 2.

1 kilogrammes, to help you approach the problem.

So pause the video now and have a go.

So we know that the total mass of the three parcels and the two envelopes is 2.

1 kilogrammes.

And we know therefore that the two envelopes have a total mass of 240 grammes.

And then the remainder is the mass of the parcels.

Remember I recommended that you convert this into grammes to help you out.

So we know that the total mass is 2,100 grammes.

The mass of the envelopes is 240.

So the difference between these two, what's left over, is 1,860 grammes.

So three parcels have a mass of 1,860 grammes.

Then one parcel has a mass of 1,860 divided by 3, which is equal to 620 grammes.

Now it's time for you to do some independent learning.

So pause the video and complete the questions and then click restart once you're finished.

So for question one, you are converting between grammes and kilogrammes, and you had your diagram here to help you out.

So grammes to kilogrammes, we are dividing by 1,000.

So the first one will be 0.

817 grammes.

And the next one will be 0.

276 grammes.

For the third and fourth, we're converting from kilogrammes to grammes, so multiplying by 1,000.

So we'll have 254 grammes and 720 grammes.

And then going from grammes to kilogrammes, dividing by a 1,000, 0.

156 kilogrammes.

Back the other way, we have 874 and 623.


Then 305 grammes is equivalent to 0.

305 kilogrammes.

Remember that place holder needed to come over.

And finally 0.

3 kilogrammes is equivalent to 300 grammes.

Next question, we have an eight week old puppy, which is put on the scales.

So looking at the scales, we can see that the puppy has a mass of 4.

1 kilogrammes.

Six months later, the puppy weighs 8.

7 kilogrammes more.

So we needed the mass of the puppy in grammes.

So the original mass was 4.

1 kilogrammes, plus the 8.

7 kilogrammes, gives us a mass of 12.

8 kilogrammes.

But the answer was asked for in grammes.

So 12.

8 multiplied by 1,000 is equal to 12,800 grammes.

In question three, a pirate finds some gold bars and he needs to know how many grammes of gold he has in order to sell them.

He weighs one third of the bars, and we need the total mass in grammes.

So again, this is pointing to 4.

1 kilogrammes.

That's one third.

So to find the total, we need to multiply that by 3, to find three thirds or the whole.

Which gives us 12.

3 kilogrammes.

And then again, we're asked for the answer in grammes.


3 multiplied by 1,000 is equal to 12,300 grammes.

Final question.

I hope you're appreciating my good names for animals in the last couple of slides.

So I have been tracking the weight of my new kitten, Apricat.

And at the end of week one, Apricat had gained 380 grammes.

At the end of week two, 0.

09 kilogrammes.

And at the end of week three, 0.

27 kilogrammes.

Apricat now weighs 2.

01 kilogrammes.

So I want to know his weight at the beginning in grammes.

So either all of these needed to be converted to grammes initially, or just the first one, 380 grammes into kilogrammes, so that we're dealing with all of the same units.

And that's how I approached it.

So I called Aprcat's initial weight as, a.

And then added the 380 grammes in kilogrammes, which is 0.


And then the other two weights, to get his current weight of 2.

01 kilogrammes.

So I know that the original weight, a, plus 0.

74 kilogrammes, which is these three numbers added together, gives me 2.

01 kilogrammes.

And I need to use the inverse.

So 2.

01 kilogramme subtract 0.

74 kilogrammes, will give me, a, which is 1.

27 kilogrammes.

And then I wanted it in grammes, so multiply by 1,000 to give me 1,270 grammes.

Time for your final quiz.

So pause the video and complete the quiz and then click restart once you're finished.

In our next lesson, we'll be solving problems involving the calculation of measure.

I'll see you then.