Circumference and Area of Circles

Math 7

Vocabulary• A circle is a set of points

in a plane that are the same distance from a given point, called the center.

• The distance from the center to any point on the circle is called the radius. (r)

• The distance across the circle through the center is called its diameter. (d)

• d = 2r• The distance around the

circle is called the circumference.

Find the circumference of each circle.C = d or C = 2 r

Use 3.14 for pi ( )

Let's VoteFind the radius of

a circle with a diameter of 6 inches.

a. 6 inches

b. 3 inches

c. 12 inches

d. 36 inches

Find the circumference of a circle with a diameter of 10 centimeters. Round to the nearest tenth.

a. 314.2 cmb. 78.5 cmc. 31.4 cmd. 15.7 cm

Find the circumference of a circle with a radius of 9 centimeters. Round to the nearest tenth.

a. 56.5 cm

b. 28.3 cm

c. 18 cm

d. 4.5 cm

Which measure is closest to the circumference of the dream catcher shown below?

a. 7.9 in.b. 15.7 in.c. 34.1 in.d. 62.8 in.

Area of a CircleThe area of a circle is equal to times the

square of the radius (r). A =

Find the area of the circles.

r2

Find the area of the circle.

a. 615.8

b. 44.0

c. 22.0

d. 153.9

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• Find the area of the circle. Round to the tenths place.

a. 254.3

b. 28.3

c. 63.6

d. 56.5

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A bicycle tire has a radius of 12 inches. How far will the bicycle travel in 20 rotations of the tire? Round to the nearest tenth.

a. 75.4 in.

b. 1507.2 in.

c. 753.4 in.

d. 452.2 in.

A dog is leashed to a point in the center of a yard, so the area the dog is able to explore is circular. The leash is 25 feet long. What is the area of the region the dog is able to explore? Round to the nearest tenth.

a. 78.5

b. 490.6

c. 157

d. 1962.5

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