Question

a roller 140 cm long has a radius of 35cm.to level the playground it takes 980 complete revolutions. Determine the cost of levelingthe playground at the rate of 75paisaper square metre

Answer 1

For the roller,
height, h = 140 cm = 1.4  m
radius, r = 35 cm = 0.35 m

The roller takes 980 revolutions to level the playground. 
Thus, Area covered by roller = Area of playground.

∴Area of playground = 980 * Curved Surface Area of Roller
                                  = 980 * 2πrh
                                  = 980 * 2 * 22/7 * 0.35 * 1.4
                                  = 21128.8 / 7 
                                  = 3018.4 m²

Thus, area of the playground is 3018.4 m²

Area                         Cost
1m²                          75 paise = Rs 0.75
3018.4 m²                   (?)

= 3018.4 * 0.75
= Rs. 2263.8

Thus, the cost of levelling the playground should be Rs 2263.8

Answer 2

surface area of the roller = 2πrh
                                           = 2 × 22/7 × 35 × 140
                                           = 30800 sq.cm
surface area of the play ground = 980 ×30800
                                                      = 30184000 sq.cm
                                                      = 3018.4 sq.m
cost of leveling the play ground = 75 × 3018.4 paise
                                                      = 226380 paise
                                                      = 2263.8 rupees