McGraw Hill Math Grade 8 Lesson 21.3 Answer Key Circles

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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 1
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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 2
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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 3
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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 4
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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 5
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?
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 6
Answer:
OA,OB,

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

SOLVE

Question 1.
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 7
What is the area of the circle? ___________
What is the circumference? ___________
Answer:
The area of the circle is 314.285 cm2,
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 = π r², A = 3.14285 X 10 cm X 10 cm = 314.285 cm2 and circumference of the circle is C = 2πr = 2 X 3.14285 X 10 cm = 62.857 cm.

Question 2.
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 8
What is the circumference of the circle? ___________
What is the radius? ___________
Answer:
The circumference of the circle is 14 π,
The radius is 7,

Explanation:
Given the area of the circle as 49π as we know area of the circle as A = π r²,
49 π = π X r X r, So r= square root of 49 so r = 7 and as circumference of the circle is C = 2πr = 2 X π X 7 = 14π.

Question 3.
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 9
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 cm2,
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 = π r², A = 3.14285 X 5 cm X 5 cm = 78.57125 cm2 and circumference of the circle is C = 2πr = 2 X 3.14285 X 5 cm = 31.4285 cm.

Question 4.
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 10
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 is  113.1426 cm2,

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 = 2πr = 2 X 3.14285 X 6 cm = 37.7142 cm and area of the circle as A = π r², A = 3.14285 X 6 cm X 6 cm = 113.1426 cm2.

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 = 2πr = 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.)
McGraw Hill Math Grade 8 Lessons 21.3 Answer Key Circles 11
_____________ π km
Answer:
Longer is route B than route A is 10π 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 2πr as r is 5 km so it is 2 X π X 5 km = 10π km and circumference of route B is 2πr as r is 10 km so it is 2 X π X 10 km = 20π km therefore longer is route B than route A is 20π km – 10π km = 10π km.

Leave a Comment

Scroll to Top
Scroll to Top