Find
(i) the lateral or curved surface area of a closed cylindrical petrol storage tank that is 4.2 m in diameter and 4.5 m high.
(ii) how much steel was actually used, if 1/12 of the steel actually used was wasted in making the tank.
(i) Radius of the tank (r) = 4.2/2 m = 2.1 m
Height of the tank (h) = 4.5 m
Curved surface area = 2πrh m2
= (2 × 22/7 × 2.1 × 4.5) m2
= 59.4 m2
(ii) Total surface area of the tank = 2πr(r + h) m2
= [2 × 22/7 × 2.1 (2.1 + 4.5)] m2
= 87.12 m2
Let x be the actual steel used in making tank.
∴ (1 – 1/12) × x = 87.12
⇒ x = 87.12 × 12/11
⇒ x = 95.04 m2
