Circles: Finding the Area and Circumference

Circles: Finding the Area and Circumference

By LESLEY ELBERT

​Parts of Circles

A circle is a set of all points equidistant to a center.

​

r = radius, d = diameter

​

Diameter: d=2r

​

Radius: ​r= d÷2

Some text here about the topic of discussion

Multiple Choice

What is the diameter?

• 8
• 16
• 10
• 4

Multiple Choice

What is the radius?

• 18
• 72
• 38
• 14

Multiple Choice

What is the diameter of this circle?

• 3.5
• 3
• 5
• 7

Multiple Choice

What is the radius if the diameter is 27?

• 135
• 13.5
• 1.35
• I do not know

Multiple Choice

If the diameter of the large circle is 36 cm, what is the radius of each of the small circles?

• 12 cm

• 18 cm

• 24 cm

• 6 cm

Finding Circumference and Area

Circumference:

C = πd or C = 2πr

​

Area:

A = πr²

Multiple Choice

Find the circumference of the circle.

• 31.4 cm

• 78.5 cm

• 314 cm

• 15.7 cm

Multiple Choice

Find the circumference of the circle.

• 38.47 cm

• 10.99 cm

• 43.96 cm

• 21.98 cm

Multiple Choice

I wrapped a tape measure around the trunk of the tree and it was 14.13 feet. What is the diameter of the tree? Use 3.14 for pi. Round to the nearest hundredth.

• 2.25 ft

• 44.37 ft

• 4.5 ft

• 17.27 ft

Multiple Choice

Find the area of the circle

• 43.96 units²

• 153.86 units²

• 87.82 units²

• 307.72units²

Multiple Choice

What is the area of this circle?

• 452.39 cm²

• 139.12 cm²

• 113.1 cm²

• 84.23 cm²

Fill in the Blanks

Shring's dining room table is round and has a radius of 4.5 feet. What is the tabletop's area?

Round to the nearest tenth.

Multiple Choice

A _____ is half of a circle.

• circumference

• pi

• semicircle

• composite figure

Fill in the Blanks

Mrs. Wilson placed the welcome mat shown below on her front door step. What is the area of her welcome mat in square feet? Round to the nearest tenth. Please label like this - square in or sq in)

Fill in the Blanks

A glass stained window is shaped like a semicircle. The bottom edge of the window is 36 inches long. How much colored glass would you need to cover the stained window? Round to the nearest tenth. (please label - sq inches or sq in)

Multiple Choice

A circular apple pie has an area of 706.5 cm². What is the radius of the pie? Use 3.14 for pi.

706.5= $$\pi r^2$$  

• 225 cm

• 112.5 cm

• 15 cm

• 30 cm

Poll

How do you feel about today's lesson?