Question 1: Calculate the surface area of a sphere with a radius of 3 cm.

Answer: 113.1

Question 2: Find the surface area of a sphere with radius 5 cm, using π ≈ 3.14.

Answer: 314

Question 3: Calculate 4πr² when r = 7 cm, using π = 3.14.

Answer: 615.44

Question 4: A sphere has a radius of 10 cm. Calculate its surface area using π ≈ 3.14.

Answer: 1256

Question 5: A globe has a radius of 12 cm. Find its surface area.

Answer: 1809.6

Question 6: A spherical ball has a surface area of approximately 251.3 cm². Find its radius.

Answer: 2

Question 7: Construct a sphere with a radius of 4 cm on the grid. Then, calculate its surface area.

Answer: Approx. 201.06

Question 8: A toy is a sphere with a radius of 6.5 cm. Calculate its surface area using π ≈ 3.14.

Answer: 265.7

Question 9: A spherical tank has a radius of 8 meters. Calculate the surface area and compare it to the value obtained using π ≈ 3.14 and π ≈ 3.1416. Show your working.

Answer: Approx. 804.2; 804.2 (rounded to 1 decimal place)

Question 10: A mistake was made in calculating the surface area of a sphere with radius 9 cm: the answer given was 1020 cm². Identify and correct the error.

Answer: Incorrect approximation of π or calculation mistake; correct surface area is approximately 1020 cm² when using π ≈ 3.14, but check the calculation steps.

Question 11: Challenge: Derive the formula for the surface area of a sphere starting from the formula for the surface area of a circle and explain each step.

Answer: The surface area of a sphere is derived by revolving a semicircular cross-section; integrating the circumference 2πr about the axis results in 4πr².