8.1 Circumference of Circles Math Wars

8.1 - Circumference of Circles

Objective:  Students will use diameter and radius to find the circumference of circles.

​The next few questions are a review of previous concepts.

Math Response

Elena takes her younger cousin to ride on a merry-go-round at a fair. The top of the merry-go-round is shaped like a regular octagon. Each side of the octagon is 4.5 feet. Find the area of the merry-go-round. 

Round to the tenths place.

Type answer here

Correct Answer: 100.8

Deg^°

Rad

Math Response

Find the area of the shape above

Type answer here

Correct Answer: 52

Deg^°

Rad

​Circumference is the distance around a circle (perimeter).

Multiple Choice

The definition of circumference is

• distance from the center of any point on the circle

• distance from one point to another

• distance around the circle

• distance from the center of any point on the circle

Multiple Choice

Which part of the circle is the black line?

• Diameter

• Radius

• Circumference

• Center

• Chord

Multiple Choice

Which part of the circle is the red line?

• Diameter

• Radius

• Circumference

• Center

• Chord

Multiple Choice

Which part of the circle is the purple line?

• Diameter

• Radius

• Circumference

• Center

• Chord

Multiple Choice

What is the formula for finding the circumference of a circle?

• C = r²

• C = rd

• A = π·r²

• C = π·d

1. ID diameter or radius.

2. Write the formula.

3. Substitute and solve.

​Find the circumference of the circle. Use 3.14 for π.

​You do:
Find the circumference of the bottle cap. Use 3.14 for π. Round to the nearest hundredth if necessary.

​Find the circumference of a circle with a radius of 0.9 centimeter. Use 3.14 for π.

Multiple Choice

Is the red line a radius or diameter of the circle?

• Radius
• Diameter

Multiple Choice

What is the formula for finding the circumference of a circle?

• C = r²

• C = rd

• A = π·r²

• C = 2⋅π⋅r

​Find the circumference of a circle with a radius of 3.7 meters. Use 3.14 for π. Write your answer as a decimal rounded to the nearest hundredth.

​Find the circumference of the circle. Use 3.14 for π. Round your answer to the nearest hundredth.

Let's Practice.

Math Response

​Find the circumference of the circle. Use 3.14 for π. Round your answer to the nearest hundredth.

Type answer here

Correct Answer: 39.25

Deg^°

Rad

Math Response

Steven purchases a bowl. The diameter of the bowl is 14 cm. What is the circumference of the bowl? Use 3.14 for π.

Round to the nearest hundredth.

Type answer here

Correct Answer: 43.96

Deg^°

Rad

Multiple Choice

Alex has trained his puppy, Popper, to jump through a ring. According to Alex's measurements and calculations, the ring has a diameter of 3.5 feet. What is the ring's circumference (use 3.14 for pi)?

• 11.32 ft
• 12.25 ft
• 10.99 ft
• 8.75 ft

Math Response

What is the circumference of a circle with a diameter of 5 in? Use 3.14 for π.

Round to the nearest tenth.

Type answer here

Correct Answer: 15.7

Deg^°

Rad

Math Response

What is the approximate circumference of a plate with a diameter of 10 inches? Use 3.14 for Pi.

Round to the nearest hundredth.

Type answer here

Correct Answer: 31.40

Deg^°

Rad

Multiple Choice

If the diameter of a circle is 50 yards, the radius is _____

• 100 yards
• 25 yards
• 150 yards
• 15 yards

Math Response

What is the circumference? Round to the nearest tenth

Type answer here

Correct Answer: 113.1

Deg^°

Rad

Math Response

What is the circumference?

Round to the nearest hundredth.

Type answer here

Correct Answer: 113.04

Deg^°

Rad

Drag and Drop

The Jones family wants to enclose their circular garden with a fence. To the nearest foot, what is the minimum length of fencing they need to buy?

Placeholder

Drag these tiles and drop them in the correct blank above

56.25 ft

246 ft

365 ft

393 ft

Multiple Select

What two formulas can you use to find the circumference?

• C = π·d

• C = π·r²

• C = 2·π·r

• C = d²

Multiple Choice

Find the circumference of the circle.

• 12ft

• 24ft

• 37.68ft

• 75.36ft

Math Response

Find the circumference of the circle given.

Round to the nearest tenth.

Type answer here

Correct Answer: 31.4

Deg^°

Rad

Multiple Choice

Find the circumference of a circle with a radius of 13.5 mm. Use 3.14 for π.

• 37.68mm
• 18.84mm
• 84.78 mm
• none of the above

Multiple Choice

Find the circumference of a circle with a radius of 12.5 mm.

• 37.68mm

• 18.84mm

• 78.5mm

• none of the above

Multiple Choice

Randy’s circular garden has a radius of 1.5 feet. He wants to enclose the garden edging that costs $0.75 per foot. About how much will the edging cost? Use 3.14 for π.

Hint: Find the length of the fencing first.

• $8.00
• $7.00
• $3.50
• $0.50

Drag and Drop

The Jones family wants to enclose their circular garden with a fence. What is the square footage of space within the fence to the nearest foot?

Placeholder

Drag these tiles and drop them in the correct blank above

393 ft2

3066 ft2

3906 ft2

12266 ft2

Multiple Choice

What is the diameter?

• 8
• 16
• 10
• 4