The base area of a right circular cone is 21m and height is 14m . Calculate the expenditure to colour the curved surface at the rate of rs. 1.50 per sq.m.

Explanation

The diameter of the base of the cone =21 metres.
`therefore` the radius of the base of the cone `=(21)/(2)` metres.
The height of the cone `=14` metres.
`therefore` the slant height of the cone `=sqrt((14)^2+((21)/(2))^2)"metres"=sqrt(196+(441)/(4))"metres"`
`=sqrt((784+441)/(4))"metres"=sqrt(1225)/(4)"metres"=(35)/(2)"metres"`.
`therefore` the curved surface area `=(22)/(7)xx(21)/(2)xx(35)/(2)"sq-metres"=577.5sq-m`.
So, the expenditure to colour the curved surface area at the rate of `rs 1.50` per sq-m `=rs 577.5xx1.50= rs 866.25`.
Hence the required cost `= rs 866.25`.