The radius of a hollow sphere is 21 cm. It is cut into two equal halves by a plane passing through its centre. What is 75% of the curved surface area (in cm2, rounded off to the nearest tens) of the hemisphere? (take $π =\frac{22}{7}$)
Answer & explanation
Correct answer: option 3
We know that,
CSA of the hemisphere = 2πr2
We have,
The radius of a sphere is 21 cm
When a sphere is cut from its center, we will get a hemisphere,
CSA of the hemisphere = 2 × \(\frac{22}{7}\) × 21 × 21 = 2772 cm2
Now, 75% of the CSA of hemisphere = 2772 × 75%= 2080 cm2