# Lesson video

In progress...

Hello everyone.

And welcome to Maths with Ms. Dobrowolski.

In this lesson, we'll be applying addition and subtraction of measurements.

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

First, we'll have a go at estimating, then you'll be ready for your talk task.

Then we'll look at addition and subtraction of mass, and finally, you'll be off for your independent tasks.

For this lesson, you will need a pencil and a notebook.

If you don't have these items, pause video now and go get them.

Super.

For estimating.

What does it mean to estimate? Do you know? It means to make a sensible guess.

Not something outrageous, but sensible.

So for example, the mass of an apple is about 20 grammes.

So if you have an apple, hold it in your hand, I unfortunately don't have an apple, the closest I have is 11.

So if you have another piece of fruit, this would work as well.

So the mass of an apple is about 20 grammes.

Can you find anything else that feels just this heavy? Unfortunately, I don't have anything else, but you can use this to estimate the weight of another object.

So what I'd like for you to do today is I want you to find some items in your home that have the mass listed on the package.

So anything that has a packaging around it.

What I'd like for you to do, is to estimate the mass.

So if we know that this piece of fruit is about 20 grammes, I can hold the other object in my hand and I can estimate.

Well, this bag of pasta is a bit heavier to me, it feels a bit heavier than this piece of fruit.

So I estimate the mass is, oh, I don't know, 200 grammes.

Okay.

So now I check the mass.

Oh, that says 500 grammes.

So the mass of this is 500 grammes.

So you can do that with some other items in your house.

Anything that has a package will have the mass listed on it.

So pause the video now, see if you can find some items and estimate their mass, and then I'll see you when you're finished.

Good luck! Super.

So I hope you were able to find some items in your home where you can estimate the mass.

Again, you have probably lots of different foods than I do.

So you had some different packages compared to me.

Now, what we can do is order these from heaviest to lightest.

So I have four different types of fruits here, and I want to order them from the heaviest fruit to the lightest fruit, and I'm going to use my greater than symbols to help me.

So let's see.

What is the heaviest that we see? Is it the apple for 23, the orange for 29, the banana that's 19 grammes or the pear that's 32 grammes.

The heaviest item is the pear that weighs 32 grammes.

What is the next heaviest item? Good.

The orange that weighs 29 grammes.

So the pear, 32, is greater than 29, which is greater than 23, which is greater than 19.

So the banana is the lightest item.

19 grammes is less than 23 grammes, right? So the banana is the lightest.

Now, for this activity, I want to find the total mass of the banana and the orange.

So the banana and the orange, if I want to find the total mass, I have to put my parts together to get my whole.

So that means I need to add 41 and 42.

So in order to make this easier, I've partitioned my 41 and 42 into tens and ones.

So 40 plus 1 and 40 plus 2, let's add the tens first.

40 plus 40 is equal to 80.

And then one plus two is equal to three.

So 80 plus 3 is equal to 83 grammes.

So the total mass of the banana and the orange is 83 grammes.

What if I want to find the difference in mass between the pear and the apple? So the pear is 40 grammes and the apple is 55 grammes.

So I want to find the difference between 55 and 40.

So what I'm going to do is use my strategy of counting on, so I'll start at 40.

I know 40 plus 10 is equal to 50 and then 50 plus five is equal to 55.

So in between 40 and 55, I have 10 plus five, which is equal to 15 grammes.

The difference between 55 and 40 is 15 grammes.

So for your independent task, I've given you the masses of four different fruits.

So you have to use these, the mass of the apple, the banana, the orange, and the pear, to answer the following questions.

Remember, these are the numbers you need to use to answer all of these questions.

So for example, the heaviest fruit is, which of these fruits is the heaviest? That's what you need to answer.

So pause the video, and resume when you're ready to go over the answers.

So the heaviest fruit is the apple.

The lightest fruit is the orange.

Now, to put them in order from lightest to heaviest, we have to start with the orange because that was only 14 grammes, it only had a mass of 14 grammes.

So the orange was less than the banana, which was less than the pear, which was less than the apple.

So the apple was the heaviest.

Then here we compare two fruits.

I said, the apple is heavier than the pear.

It had, its mass was a greater value than the pear.

Then there were a couple of different options here.

You could have also said, the apple was heavier than, or greater than the banana or the orange even.

As long as you add a fruit here that had a greater mass than the fruit you put on the other side of the greater than symbol.

For example, you could have also said, the pear has a greater mass than the banana.

And so on and so forth.

To find the total mass of the banana and pear, you had to add the banana and the pear.

So 15 plus 18 is equal to 33.

Find the difference between the heaviest and lightest fruit.

So the heaviest was the apple for 20 grammes and the lightest was the orange for 14 grammes.

20 minus 14 is equal to six.

Then to find the total mass of all four fruits, I added 20, plus 18, plus 15, plus 14, which was equal to 67 grammes.

Great job, everyone.

If you'd like to, you can ask your parent or carer to share your work on Instagram, Facebook, or Twitter, tagging @OakNational and #LearnwithOak.

As always, don't forget your final quiz.

And I really hope to see you for future lessons.

Bye.