Question

21 cylindrical pillars of a building have to be cleaned. if the diameter of each pillar is 50 cm and the height is 4m, find the cost of cleaning them at the rate of Rs. 1.50 per m sq.?

Answer 1

Given : Diameter of the pillar = 50 cm, so the radius = 25 cm or 0.25 m
Height of the pillar = 4 m
Curved surface area of the pillar = 2*π*r*h
= 2 × 22/7 × 0.25 × 4
= 44/7
= 6.285 sq m
Curved surface area of one pillar = 6.285 sq m
The curved surface area of 21 pillars = 21 × 6.285 = 131.985 sq m
The cost of cleaning = Rs. 1.50 per sq m
Total cost of cleaning of cleaning 21 pillars = 1.5 × 131.985
= Rs. 197.97 or Rs. 198
Total cost of cleaning the 21 pillars is Rs. 198
Answer.

Answer 2

Given

diameter = 50 cm

height = 4 m

no. of pillars 21

cost of cleaning 1= 1.50

radius = half of diameter = 50cm÷2 = 25 cm.

converting cm in m : 0.25 m

now ,as we know curved surface area= 2πrh

2×22/7×0.25×4 = 6.28m^2

now 6.28 × no. of pillars

6.28 × 21=132m^2

cost= cost of 1 pillar cleaning × 132

= 1.50×132= 198

hence ₹ 198 is answer.

hope it helps u