McGraw-Hill Education GRE 2019

Pi (π) might appear intimidating, but it’s simply a constant. Its value is roughly

3.14. For the GRE, though, almost any question that involves π will expect you to

represent your answer using π instead of a decimal. For example, if you are asked

to solve for the circumference of a circle with a diameter of 8, the answer would be

8π instead of 8 × 3.14 = 25.12.

What is the radius of a circle whose circumference is 24π?

A 6

B 12

C 18

D 24

E 30

SOLUTION: Use the circumference formula:

π(d) = 24π

24 = d

Since the radius is half of the diameter, the radius of the circle is 12.

The correct answer is B.

The next element of a circle that you can calculate using radius and diameter is the

area. The area of a circle represents the amount of space within that circle.

The formula for area of a circle is πr^2.

If a circle has a circumference of 16π, what is its area?

A 4π

B 8π

C 16π

D 64π

E 256π

SOLUTION: To solve for the circle’s area, you need to determine the radius. Use

the formula for circumference to determine the radius:

16π = πd

d = 16

Since d = 2r, r = 8. Substitute 8 for r in the area formula: area = π8^2 = 64π.

The answer is D.

CHAPTER 13 ■ GEOMETRY 409

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