Question

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 litre. [Use $\pi =\frac{22}{7}$].

Answer 1

Given: $h=24$ cm

Upper radius = $r_1=20$

Lower radius = $r_2=8$

Volume of frustum of a cone = $\frac{1}{3}\pi h[r_1^2+r_2^2+r_1{r}_2]$

= $\frac{1}{3}\times \frac{22}{7}\times 24[{20}^2+8^2+20\times 8]$

= $15689.14$ $c{m}^3$

= $15.69$ litre

The cost of milk which can completely fill the container at the rate of $Rs.21$ per litre = $21\times 15.69=Rs.329.49$