Question

A hemispherical dome of a building is to be painted. The circumference of the base of the dome was 17.6m .Find the cost of painting it at the rate of rs.5 per 100 sq. cm

Answer 1

Let radius of dome be r
Circumference of dome = circumference of the hemisphere
Let radius of dome be r
17.6 =2×22÷7× r
Therefore r=2.8m
r= 280cm
Curve surface area = 2×22÷7×280×280 =492800cmsquare
Cost of 1cmsq =5×1÷100
Therefore cost of 492800cmsq = 5×1÷100×492800
Therefore cost of Painting dome is Rs 24640

Answer 2

circumference of base = 17.6 m
since circumference of base = 2×pi×r
=> 17.6 m = 2×pi×r
=> 17.6 m = 2×22/7× r
=> r = 2.8 m

surface area of the dome
= 2×pi×r^2
= 2×22/7×2.8 ^ 2 m^2
= 2×22/7 × 7.84 m^2
= 49.28 m^2
= 4928 cm^2

therefore,
the cost of painting it at the rate of 5 rupees per 100 sq. cm = 4928 / 100 × 5
= 49.28 × 5 rupees
= 246.4 rupees