Lesson video

Hello, my name is Miss Parnham.

And in this lesson, we're going to learn how to draw and interpret pie charts.

A pie is a circular chart invented by Florence Nightingale in order for her to show her statistics.

And we're going to start with a very simple example for these lunch choices.

So if we total the frequency, we have 16 so, what we can do is draw a circle and divide it equally into sixteenths quite easily.

So the pasta, because he has a frequency of five, we can form a sector made from five sixteens and we label that, pasta.

And the pizza is found from seven of sixteens form in that sector.

And the risotto and salad will be the same size they're both two sixteens each, and that will complete the circle.

Notice that we label each sector and we can see on a pie chart straight away, the model lunch choice, it was pizza because that's the largest sector.

This time we're going to construct a pie chart using angles and we'll need a protractor to do that.

So look at this data, we have four different types of bird and their frequencies.

The first thing we need to do is add up those frequencies and their total 45.

And we know that in a pie chart, the sectors all have angles, which total 360 every single time.

So we divide 360 by 45 and work out that it is eight degrees per bird.

So we will take that amount and multiply by our frequencies to find the angle of each sector.

So we have 136, 64, 88 and 72 degrees.

And if we add those four angles together, they do indeed some to 360 degrees.

Now we need to take a protractor to construct a pie chart, and it can be a complete circle or semicircular protractors are fine for this as well.

When we construct pie charts, we always start with a vertical line from the centre of the circle to the circumference.

If you want to think of it as pointing North, you can do.

And we will always measure clockwise when we construct our sectors.

So the first one is going to measure 136 degrees.

So central the protractor on the centre of the circle, zero degrees at the top and measuring clockwise to 136 degrees and then we rule the line from the centre to where we had 136 degrees.

And we know that there.

And then rotate the protractor so that zero moves around to the last straight line that you drew at 136 degrees.

And we're going to measure clockwise from that point to 64 degrees.

And then we're going to rule a line to that point.

And that forms our next sector which we can level with Robin.

Then rotating the protractor again so that zero is on the last straight line that we drew, we're going to measure 88 degrees clockwise from that point and label that Goldfinch.

Drawing that line in, I'm labelling that with 88 degrees.

Now what we should have left is, 72 degrees and you can check that with a protractor and our final sector can be labelled Dunnock.

Here's a question for you to try.

Pause the video to complete the task and then restart the video when you've finished.

Here are the answers.

"You never have to actually draw the last sector of a pie chart because it always completes a circle.

But we can check it is the size it should be, and that can reassure us that everything else is correct.

Here's a question for you to try.

If you don't have a protractor, then you can always attempt the first part of the question by completing the table.

Pause the video to complete the task, and then restart the video when you're finished.

Give me the answers.

We have a total frequency of 40 in this example.

So 360 degrees divided by 40 means that 90 degrees per person.

So we take those frequencies and multiply them by nine to get the angle of each sector.

And when you construct each sector, you should be left with a 45 degree gap which you can just label with Vanilla.

In this example, we're going to interpret information provided in a pre-drawn pie chart.

Here we have 168 degrees, 78 degrees and 48 degrees for three of these species, and we can place that in the table.

We've not been given the angle for the Coot, but we can work it out because all the angles of all four sectors, most sewn to 360 degrees.

So let's subtract what we know away from 360 degrees, and that leaves 66 degrees which we can fill in the table.

Our next step is to find out how many degrees represent one bird.

And the way that we do that is by using the frequency of Mallards and the angle.

So if we divide the angle by the 28 Mallards that will tell us how many degrees per one bird and that is 6 degrees.

So to each of our angles, we will divide those by six, and this will tell us the frequency for each type of bird, 13 Swans, eight Moorhens and 11 Coots.

And the question actually says, "How many birds were in the survey?" So if we add that frequency column up, we have a total frequency of 60.

And if you notice, we could have then divided 360 by six to get 60.

And that would have found the answer as well.

Here's a question for you to try.

Pause the video to complete the task and then restart the video when you're finished.

Here are the answers.

Brown eyes are easy to find a frequency for because we can see exactly 1/2 of the pie chart so, 1/2 of the total frequency of 60 is 30.

With the others, for the blue eyes, we can divide 360 by 60 to get six degrees per person and 72 degrees divided by six degrees gives us the 12 and the green and hazel eyes are the same, and they total 108 degrees, so there are 54 degrees each and dividing that by six it says nine for our frequency.

Here's another question for you to try.

Pause the video to complete the task and then restart the video when you're finished.

Here are the answers.

10 purchases equates to 40 degrees on the pie chart, which must mean four degrees per purchase.

So all the angles are divided by four to find the frequency of each craft genre and 360 degrees divided by four is 90 if you interested in the total frequency there.

That's all for this lesson, thank you for watching.