Question

The internal and external diameter of a hollow hemispherical vessel are 26cm and 30 cm find the coay of painting the vessel all over at 21 paise perm2

Answer 1

Internal diameter = 26 cm

=> Internal radius = 26/2 = 13 cm

Similarly, outer radius = 15 cm

We know that,

SA of Hemisphere = 2πr²

=> Internal SA = 2π(13²)

Outer SA = 2π(15²)

Since, it's a hollow hemisphere, a ring will also be formed on the top. So, it will also be painted.

Area of ring = πR² - πr²

Where, R = outer radius and r = inner radius.

=> π(15² - 13²)

= π(15 - 13)(15 + 13)

=> 2π(28)
Now total SA =
2π(13²) + 2π(15²) + 2π(28)

=> 2π(13² + 15² + 28)

=> 2π(169 + 225 + 28)

= 2π(422) m²


So cost of painting = 21 paise per m²

= 2π(422) × 21 paise

= 2 × 22/7 × 422 × 21

= 55704 paise

=> 55704/100 rupees

= ₹557.04

Answer :- 557.04