The diameter of a roller, `120 cm` long, is `84 cm.` If it takes `500` complete revolutions to level a playground, find the cost of leveling it at `Rs 5` per square metre.

Explanation

Radius of the roller, `r = 42 cm`, and its length, `h = 120 cm`
Area covered by the roller in `1` revolution
= curved surface area of the roller
`= (2pi rh)` sq units
`= (2 xx (22)/(7) xx 42 xx 120) cm^(2) = 31680 cm^(2)`
Area covered by the roller in 500 revolutions
`(31680 xx 500) cm^(2) = ((31680 xx 500)/(100 xx 100)) m^(2) = 1584 m^(2)`
`:.` area of the playground `= 1584 m^(2)`
Cost of levelling the playground `= Rs (1584 xx 5) = Rs 7920`