Lesson video

Hello everyone, it's Mr. Millar.

Hopefully you're doing well.

Today's lesson we're looking at Percentages of Amount.

We had a look at this last time.

We're going to look at it in a slightly different way today.

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

Okay, so for the try this task, we have a double number line.

So, in this double number line, the top line represents the quantity.

So you can see you've got 0 and 220, so 220 is 100%.

And the bottom line represents the percentage.

And you've got a couple of percentages on there already, and you can see that they go up in tenths.

So, what you are trying to do is you're trying to find out these two missing values here.

There's a clip in the speech bubble, to find 30% of 220, I can first find 10% and then multiply by something.

So what do you think that is? And how do you think you can work out 30% of 220? Pause the video for a minute or two to see if you can work this one out.

Okay, perfect.

So if you've thought that you can find 10%, and finding 10% of something is really easy, you just divide it by 10.

So that's going to be 22.

And then to get from 10% to 30%, you're going to have to multiply it by 3, because 30% is obviously 3 times bigger than 10%.

So multiplying by 3 here, and 22 times by 3 is going to give me 66.

So, in the previous lesson to find the percentage of an amount, we used a bar model and we used fractions to help us.

Here is a different method.

We found 10% first, and then we multiplied by 3 to get 30%.

Let's have a look at some more examples.

Okay, so again, I've got the same double number line.

I've got percentages on the bottom and values on the top.

So 70%, 35% and 95%.

How do you think you might find these percentages? So let's start off with finding 10% first, which we found out was 22.

If we know what 10% is, how can we find out what 70% is? Which is going to be here.

What would we have to multiply by? Well, we're going to have to multiply it by 7.

22 times by 7, which you can work out to be 154.

How about 35%? It's a little bit trickier.

So it's going to be here.

How do you think you might find that? Well, you could find 30% first of all, which we've already found that was 66, and then we need to get another 5%.

How might we find out 5% of 220? Well, if we know that 10% of 220 equals 22, then we can easily work out what 5% of 220 is.

What would that be? Well, that would just be 11 because we're dividing by 2.

So to find out 35%, I'm going to want to find 30% which is 66, and then I'm going to need to add another 11 which is 5%.

So that is going to be overall 77.

So just to recap what I did.

To find 35%, I first found 10% which was 22.

I then found 30% which was 66.

I then found 5% which was 11.

And then I added 30% and 5% to get 35% which was 77.

Okay, final one, how do you think you might find 95% of 220? Well, if you're thinking you can just find 5% again, which was 11, and then because 95% is 5% less than 100, all you can do is take away 11 from 220 and you get 209.

So you're doing 100% take away 5% which is 95%.

You could do it another way, you could find 10% and then multiply it by 9, and then add another 5%, that would give you the same answer.

So it just depends on what your preference is and what is quickest and easiest, but this is the idea of this lesson.

Anyway, it may make sense for you to copy down these examples before the independent task, because in the independent tasks, we're going to be seeing some similar examples.

Okay, so here is the independent task.

You need to find out different percentages of 160.

So pause the video now and have a go at these problems here.

Okay, great.

Hope that you worked on this for a few minutes, and managed to find out some of the answers.

And the answers are coming up on the next slide.

Okay, so here are the answers.

And the key here of course was first of all, finding out what 10% was.

So 160 divided by 10 is 16.

So to get 40% you multiply that by 4.

To get 5% you divide that by 2 and you get 8.

So note that for the third one 45% of 160, well, for that you just need to add 40% to 5%, which you found out both of them in the first two questions, so you just add them together.

To find 150%, well, that one you're just going to need to find 100% which is 160, and 50% which was 80, and then you can add them together.

And then the final one, well, what percent of 160 gives me 168? So you have 168 up here and you have a gap of 8, and you know that looking at it down here, that a gap of 8 is 5%, so the missing percent is going to be 105%.

So that is the answer 105% to the final question, question number six.

Great, let's have a look at the explore task now.

Okay, so here is the explore task.

Use two of these number cards to complete the percentage sentence frame.

How many different calculations can you make? And how many different answers did you get? So just to make sure that this is really clear, you're looking to put two of these cards, one in the percentage, one in the amount, and you need to work out the calculation.

So for example, the first one you could do would just be 75% of 120, which you could work out to be 90.

And so that is one different calculation, and one different answer.

You need to find how many different calculations can you make, and how many different answers you get.

Pause the video and have it go, and see if you can find all of these.

Okay, great, so hopefully you had a good look at this.

And the answer is there are actually 12 different calculations that you can do.

So you could do 75% of 120, which we've done already.

You could also do 75% of 40, that would be the next one.

75% of 300.

And then you could have moved on to find 120% of 75, et cetera.

So three different calculations for 75% of something, three different calculations for 120% of something, and the same thing for 40 and 300.

So that is why there are 12 different calculations.

But, if you manage to actually work out all of the different answers, you would have found that there are only six different answers.

So 12 calculations but six different answers.

And the reason for that is if, for example, you had look at 75% of 120, and 120% of 75, they actually the same thing, They are actually both 90, so that is why you only get half the amount of different answers.

So on the next slide, I will just show you all of the different answers.

So here are all answers coming up.

So yeah, those are the six different answers, and there are, of course, 12 different calculations that we've already been through.

So I hope that you found this lesson interesting.

Thanks very much for watching, and next time we're going to be looking at increasing and decreasing an amount by a percentage.

But before that we're going to look at another way of finding a percentage of something.

So well done for keeping with us, and I will see you next time.

Thanks very much, have a nice day.

Bye bye.