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 $π =\frac{22}{7}$)

2080

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