This is one of the important question from the cbse board exam point of view because in 2014 cbse board exam this question was asked. Question number 4 from RS Aggarwal book page number 823, exercise 17C, chapter volume and surface area of solid.
A container, open at the top, is in the form of a frustum of a cone of height 24 cm with radii of its lower and upper circular ends as 8 cm and 20 cm, respectively. Find the cost of milk which can completely fill the container at the rate of 21 per liter.
Height, h=24 cm,
Upper radius, R=20 cm
Lower radius, r=8 cm
Volume of the container = [1/3] π h [R²+r²+rR]
1000 cm³=1 L
∴ the cost of the milk in the container=109.8247×21
∴ the cost of milk which can completely fill the container at the rate of Rs. 21 per litre is 329.472