Question

There are 20 cylindrical pillars in a building, each having a diameter of 50 cm and height 4 m. Find the cost of cleaning them at ₹ 14 per m².

Answer 1

Radius of each pillar, r = $\frac{50}{2}$ = 25 cm = 0.25 m (1 m = 100 cm)

Height of each pillar, h = 4 m

∴ Surface area of each pillar = $2\mathrm{\pi }rh=2\times \frac{22}{7}\times 0.25\times 4{\mathrm{cm}}^2$

Surface area of 20 pillars = Surface area of each pillar × 20 = $2\times \frac{22}{7}\times 0.25\times 4\times 20{\mathrm{cm}}^2$

Rate of cleaning = ₹ 14 per m²

∴ Total cost of cleaning the 20 pillars

= Surface area of 20 pillars × Rate of cleaning

= $2\times \frac{22}{7}\times 0.25\times 4\times 20\times 14$

= ₹ 1760