How_To_Be_Good_At_Math

STATISTICS • PIE CHARTS 293

Because it is a circle,

a pie chart is a round

angle of 360°. Each

sector that makes up the

chart takes up part of

this bigger angle.

Fractions

Each sector is also a

fraction of the chart. For

example, a sector with an

angle of 90° represents a

quarter. Together, all the

fractions add up to 1.

Percentages

Sectors may also be shown

as percentages of the whole

chart. A sector with an angle of

90° is 25 per cent. Together, the

percentages add up to 100%.

Angles

The angle of a sector is

measured from the centre in

degrees (°). Together, the

angles of the sectors always

add up to 360°.

Pie-chart sectors

The circle, or “pie”, is the whole set of data.

Each of the sectors, or slices, is a subset. If we

add up all the slices, we get the whole pie.

We can express the size of a slice as an angle,

a proper fraction, or a percentage.

360°

(^1) / 2
(^1) / 20
37%
(^1) / 5
(^1) / (^4) 25%
180°
72°
90°
18°
90°
?°
?%
115°
20%
5%
Can you work out the
mystery angle of the
third sector on this pie chart?
What’s the percentage
of the missing sector
on this pie chart?
Pie-chart puzzles
Here are two problems
to solve. Remember
that the angles of a
pie chart’s sectors
always add up to 360°,
and when expressed
as percentages the
sectors always come
to a total of 100%.
TRY IT OUT
50%
10%
8%
25%
Answers on page 320
18 + 72 + 90 + 180 = 360°^1 / 20 +^1 / 5 +^1 / 4 +^1 / 2 = 1 5% + 20% + 25% + 50% = 100%
292_293_Pie_charts.indd 293 29/02/2016 18:06