Solution :
Given that :
Height of the cylinder, h = 21 cm
Diameter of the cylinder, d = 7 cm
Radius = 3.5 cm
Number of balls fits in the cylindrical container = 3
a). The volume of the container is given by
[tex]$V = \pi r^2 h$[/tex]
= 3.14 x 3.5 x 3.5 x 21
= 807.76 cm cube
b). Volume of each tennis ball is given by :
[tex]$V=\frac{4}{3}\pi r^3 $[/tex]
[tex]$V=\frac{4}{3}\times 3.14 \times (3.5)^3 $[/tex]
= 179.50 cm cube
c). Volume of three tennis balls = 3 x 179.50
= 538.50 cm cube
Therefore, percentage of the container taken up by the three tennis ball is :
[tex]$=\frac{807.76 - 538.50}{538.50} \times 100$[/tex]
= 50 %