A cylindrical pillar has radius 21 cm and height 4 m. Find :

(i) the curved surface area of the pillar

(ii) the cost of polishing 36 such cylindrical pillars at the rate of ₹ 12 per m².

(i) Given:

Radius of cylindrical pillar = 21 cm

Height = 4 m = 400 cm

As we know that curved surface area of the cylinder = 2πrh

$= 2 \times \dfrac{22}{7} \times 21 \times 400\\[1em] = \dfrac{369,600}{7}\\[1em] = 52,800$

Hence, the curved surface area of the cylindrical pillar is 52,800 cm² = 5.28 m².

(ii) Curved surface area of 1 pillar = 5.28 m²

Curved surface area of 36 pillar = 5.28 m² x 36

= 190.08

Rate of polishing = ₹ 12 per m²

Total cost = Curved surface area of 36 pillar x Rate of polishing

= 190.08 x ₹ 12

= ₹ 2,280.96

Hence, the total cost of polishing 36 cylindrical pillars is ₹ 2,280.96.