Practice the questions of **McGraw Hill Math Grade 8 Answer Key PDF Lesson 21.3 Circles **to secure good marks & knowledge in the exams.

## McGraw-Hill Math Grade 8 Answer Key Lesson 21.3 Circles

**Exercises**

**SOLVE**

Question 1.

What is the diameter of the circle?

Answer:

The diameter of the circle is equal to 2 cms,

Explanation:

As we know the diameter of the circle is equal to 2 X radius, so as the given circle has

r = 1 cm so diameter = 2 x 1 cm = 2 cms.

Question 2.

What is the diameter of the circle?

Answer:

The diameter of the circle is equal to 14 in.,

Explanation:

As we know the diameter of the circle is equal to 2 X radius, so as the given circle has

r = 1 cm so diameter = 2 x 7 in. = 14 inches.

Question 3.

What is the radius of the circle below?

Answer:

The radius of the circle is equal to 4 ft,

Explanation:

As we know the diameter of the circle is equal to 2 X radius, so as the given circle has

d = 8 ft so radius = diameter/ 2 = 8 ft/2 = 4 ft.

Question 4.

What is the center of the circle?

Answer:

The center of the circle is d/2,

Explanation:

As we know the diameter of the circle is equal to 2 X radius so as the given circle has

diameter = 2 x radius or center, therefore center = d/2.

Question 5.

What is the radius of the circle?

Answer:

The radius of the circle is equal to 3 in.,

Explanation:

As we know the diameter of the circle is equal to 2 X radius, so as the given circle has

d = 6 in. so radius = diameter/ 2 = 6 in/2 = 3 in.

Question 6.

What are the two radii of the circle?

Answer:

OA,OB,

Explanation:

As a Radius or Radii of a circleÂ is the distance from the center of theÂ circleÂ to any point on it’sÂ circumference. So the given circle has two radii they are OA and OB.

**SOLVE**

Question 1.

What is the area of the circle? ___________

What is the circumference? ___________

Answer:

The area of the circle is 314.285 cm^{2},

The circumference of the circle is 62.857 cm,

Explanation:

Given the diameter of the circle as 20 cm as we know the diameter of the circle is equal to 2 X radius, so as the given circle has d = 20 cm so radius = diameter/ 2 = 20 cm/2 = 10 cm. We know area of the circle as A = Ï€ rÂ², A = 3.14285 X 10 cm X 10 cm = 314.285 cm^{2} and circumference of the circle is C = 2Ï€r = 2 X 3.14285 X 10 cm = 62.857 cm.

Question 2.

What is the circumference of the circle? ___________

What is the radius? ___________

Answer:

The circumference of the circle is 14 Ï€,

The radius is 7,

Explanation:

Given the area of the circle as 49Ï€ as we know area of the circle as A = Ï€ rÂ²,

49 Ï€ = Ï€ X r X r, So r= square root of 49 so r = 7 and as circumference of the circle is C = 2Ï€r = 2 X Ï€ X 7 = 14Ï€.

Question 3.

What is the diameter of the circle? ___________

What is the area? ___________

What is the circumference? ___________

Answer:

The diameter of the circle is equal to 10 cm,

The area of the circle is 78.57125 cm^{2},

The circumference of the circle is 31.4285 cm,

Explanation:

As we know the diameter of the circle is equal to 2 X radius given r = 5 cm so as the given circle has d = 2 X 5 cm = 10 cm. As we know area of the circle as A = Ï€ rÂ², A = 3.14285 X 5 cm X 5 cm = 78.57125 cm^{2} and circumference of the circle is C = 2Ï€r = 2 X 3.14285 X 5 cm = 31.4285 cm.

Question 4.

What is the circumference of the circle? ___________

What is the area of the circle? ___________

Answer:

The circumference of the circle is 37.7142 cm,

The area of the circle isÂ 113.1426 cm^{2},

Explanation:

As we know the diameter of the circle is equal to 2 X radius given d = 12 cm so as the given circle has r = 12/2 cm = 6 cm. As we know circumference of the circle is C = 2Ï€r = 2 X 3.14285 X 6 cm = 37.7142 cm and area of the circle as A = Ï€ rÂ², A = 3.14285 X 6 cm X 6 cm = 113.1426 cm^{2}.

Question 5.

A bicycle wheel measures 25 inches in diameter. How far would a bike travel if the wheel went completely around 4 times?

____________ inches

Answer:

Far would a bike travel if the wheel went completely around 4 times is 78.57125 inches,

Explanation:

Given A bicycle wheel measures 25 inches in diameter. Far would a bike travel if the wheel went completely around 4 times as we know the diameter of the circle is equal to 2 X radius given d = 25 inches so as the given circle has r = 25/2 inches = 12.5 inches. As we know circumference of the circle is C = 2Ï€r = 2 X 3.14285 X 12.5 inches = 78.57125 inches.

Question 6.

Brenda walks her dog along two circular routes laid out in the park. How much longer is Route B then route A? (Leave the answer in terms of pi.)

_____________ Ï€ km

Answer:

Longer is route B than route A is 10Ï€ km,

Explanation:

Given Brenda walks her dog along two circular routes laid out in the park. Much longer is Route B then route A is as circumference of route A is 2Ï€r as r is 5 km so it is 2 X Ï€ X 5 km = 10Ï€ km and circumference of route B is 2Ï€r as r is 10 km so it is 2 X Ï€ X 10 km = 20Ï€ km therefore longer is route B than route A is 20Ï€ km – 10Ï€ km = 10Ï€ km.