In a pie chart, the population of a city is represented by 45. If the country has a population of 10 million people, then the city's population is?

Analyzing the question

The question says the city is represented by "45" on a pie chart. A pie chart is a circle of 360°, so the "45" most likely means a sector of 45°. The country's total population is 10 million.

The concept

In a pie chart, each sector's share of the whole equals its angle divided by 360°:

Population represented = (sector angle / 360°) × total population

Solution

City population = (45 / 360) × 10 million

= (1/8) × 10 million

= 1.25 million

Checking the other options

• A (0.0045 million): would come from treating 45 as a tiny percentage, which makes no sense here.
• B (4.5 million): this comes from treating 45 as 45%, giving 0.45 × 10 million. But a pie chart is measured in degrees, not percent, unless the question says so.
• D (16 million): larger than the whole country's population, so it is impossible.

1.25 million**.

Exam tip

When a pie chart question gives a number with no unit, check whether it is an angle. Always use:

Share = angle / 360°

Simplify the fraction first (45/360 = 1/8) so the arithmetic is quick. Also eliminate any option bigger than the total, as D is here.