The average price of three items of furniture is ₹15,165. If their prices are in the ratio 3 : 5 : 7, the price of the costliest item (in ₹) is:

Volume of cone

$= \frac{1}{3}\pi r^2 h$

Given:

$6280 = \frac{1}{3} \times 3.14 \times 20^2 \times h$

$6280 = \frac{1}{3} \times 3.14 \times 400 \times h$

$6280 = \frac{1256h}{3}$

$18840 = 1256h$

$h = 15$

Now, slant height

$l = \sqrt{r^2+h^2}$

$= \sqrt{20^2+15^2}$

$= \sqrt{400+225}$

$= \sqrt{625}$

$= 25$

Curved surface area

$= \pi rl$

$= 3.14 \times 20 \times 25$

= 1570

Correct Answer: 1570