Question

150 cylindrical pillars of the Delhi Metro are to be
cleaned. If each pillar has a diameter of 84 cm and a
height of 6 m, find the cost of cleaning the pillars at a
rate of 50p per m².
​

Answer 1

Given :-

• Number of pillars = 150
• Diameter of pillar = 84 cm
• Height = 6m
• Cost of cleaning = 50 paise per m²

To Find :-

• Cost of cleaning the pillars

Solution :-

Diameter of pillar = 84 cm

Radius of pillar = D/2 = 84/2 = 42 cm = 0.42m

Height of pillar = 6m

C.S.A of pillar = 2πrh

=> 2 × 22/7 × 0.42 × 6

=> 2 × 22 × 0.6 × 6

=> 22 × 3.6

=> 158.4m²

Cost of cleaning 1m² = 50 paise

Cost of cleaning 158.4m² = 50 × 158.4m²

= 7,920 paise

OR

= Rs. 79.2