Question

A roller 150 cm long has a diameter of 70 cm , to level a playground it takes 750 complete revolution . determine the cost of leveling the playground at the rate of 75 paise per m square

Answer 1

Diameter of roller = 70 Cm
thus radius of roller, r = 35 Cm

Length of roller,      l = 150 Cm

We know area of Cylinder     A = pi * r * l
                                              A = pi * 35 * 150
                                              A = 3.14 * 35 * 150
                                              A = 16485 Cm sq
thus,   
 Area for 1 revolution = 16485 Cm sq
So
Area for 750 revolutions = 16485 * 750
                                        = 12363750 Cm sq = 1236.37 m sq

Cost for covering 1 m sq = 75 paise
thus
Cost for covering 1236.3750 m sq = 1236.3750 * 75
                                                       = 92728.1250 paise
                                                       = 927.28 rupees

Answer 2

Solution :-

Given -

Diameter = 70 cm 

Radius = 70/2 = 35 cm

Height = 150 cm

Curved Surface Area of cylinder = 2πrh 

⇒ 2*22/7*35*150

⇒ 231000/7

= 33000 sq cm

Area covered in 1 revolution is 33000 sq cm

Area of the playground in 750 complete revolution = 33000*750

= 24750000 sq cm

Area of playground in m² = 24750000/10000

= 2475 sq m

So, area of the playground is 2475 sq m

Cost of leveling = Rs. 0.75  

Total cost of leveling = 0.75 × 2475

= Rs. 1856.25 

Answer.