Find the volume (in cm
3
) of a sphere of diameter 21 cm.

Given diameter of the sphere = 21 cm.
Thus, the radius r=
2
21
​
 cm.

The formula for the volume (V) of a sphere is:

V=
3
4
​
πr
3

Using π=
7
22
​
:

V=
3
4
​
×
7
22
​
×(
2
21
​
)
3

V=
3
4
​
×
7
22
​
×
8
21×21×21
​

V=
3×7×8
4×22×21×21×21
​

Since 3×7=21:

V=
8
4×22×21×21
​

V=
8
88×441
​
=11×441=4851 cm
3