Circumference and Area of Circles

Vocabulary

100

The point at the center of a circle

Center

200

The space inside a 2-dimensional shape

Area

300

The distance across a circle through its center

Diameter

400

The distance around the outside of a circle

Circumference

500

The distance from the center of a circle to its edge

Radius

Radius, Diameter, and Formulas

100

A circle has a radius of 5 feet. What is its diameter?

10 feet

200

A circle has a diameter of 19 cm. What is its radius?

9.5 cm

300

What is the formula for circumference?

C=pid or C=2pir

400

What is the formula for area of a circle?

A=pir^2

500

A circle has a circumference of 1,099 m. What is its radius?

175 m

Find the Circumference

100

d = 1 in.

3.14 in.

200

r = 7 ft.

73.96 ft.

300

d = 9.5 cm

29.83 cm

400

r = 16.25 km

102.05 km

500

d=r+4  mm

25.12 mm

Find the Area

100

d = 1 in.

0.785 in²

200

r = 7 ft.

153.86 ft²

300

d = 9.5 cm

(Round to the nearest hundredth)

70.85 cm²

400

C = 87.92 mi

615.44 mi²

500

3d+9=45  cm

113.04 cm²

Word Problems

100

The diameter of your bike's tires is 22 inches. How far does the bike travel in one revolution of the wheels?

69.08 in.

200

A circular pizza fits perfectly in a 16 inch square pizza box. What is the area of the pizza?

200.96 in²

300

A dinner plate has a circumference of 34.54 inches. What is the diameter of the plate?

11 inches

400

Which has a larger area: 4 circles with a radius of 2 ft. or one circle with a diameter of 8 ft.?

Neither, they have the same area.

500

A dime has a diameter of 17.91 mm. A quarter has a diameter of 24.26 mm. To the nearest hundredth, how much larger is the area of the quarter?

210.21 mm²