Read and Interpret Pie Charts

Do you like to exercise?

 

 

A local gym offers four types of memberships: swim only, squash only, gym only or a full membership.

 

A gym employee analysed how many members got each type of membership and presented his findings in a pie chart:

 

 

A pie chart is a circular chart that is divided into slices (just like a pie!).

It is a handy way of representing data, especially when we are interested in what proportion of data points are within a certain group.

 

For example, in this pie chart, we can see that the most popular membership type is the full membership.

That's because the corresponding slice is the biggest one!

 

Can we tell how many members have each type of membership?

 

 

Not from the information we have!

We can only tell which one is the most popular, the second most popular etc.

 

Let's say we know that there are 720 members altogether.

How could we find how many have the gym only membership?

 

Well, we can see that the gym only slice has an angle of 90°

A full turn (both in a circle or otherwise) is 360°

The whole pie represents the total number of members, i.e. 720

 

That means:

360° = 720 members

 

But now, we want how many members 90° represents.

How could we get 90° from 360°?

We could divide by 4!

 

So we divide both sides by 4:

360° = 720 members

360° ÷ 4 = 720 ÷ 4

90° = 180 members

 

So 180 members have the gym only membership!

 

 

But now, what about if we wanted to know how many members have the full membership?

 

 

We can see that the full membership slice has an angle of 156°

 

So similarly, we set up our equations:

360° = 720 members

156° = ? members

 

But 156 doesn't go to 360!

What do we do now?

 

We get a mid-step calculation.

1° is the angle that will always work for such middle steps (but we could also use other angles if they work!).

 

To go from 360° to 1°, we divide by 360:

360° = 720 members

360° ÷ 360 = 720 ÷ 360

1° = 2 members

So each 1° represents 2 members.

 

How could we get how many members 156° degrees represent then?

We multiply 2 by 156!

1° = 2 members

156° = 312 members

So 312 members have the full membership.

 

Now grab your calculator and let's have a go at some questions!