Question

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.

Answer 1

Here, r = 4. 2/ 2  m = 2.1 m, h = 4.5 m 

(i) Curved surface area of the storage tank = 2πrh 

= 2 × 22 7 × 2.1 × 4.5 m² = 59.4 m² Ans. 

(ii) Total surface area of the tank = 2πr (h + r) 

= 2 × 22/ 7 × 2.1 (4.5 + 2.1) m² 

= 44 × 0.3 × 6.6 m2 = 87.12 m² 

Let the actual area of steel used be x m². 

Area of steel wasted = 1/ 12 of x m² = x/ 12 m². ... (i) 

∴ area of the steel used in the tank =( x − x /120 )m² = 11/ 12 x m² 

⇒ 87.12 = 11/ 12 x 

⇒ x = 87. 12x 12/ 11 = 95.04 m² 

Hence, 95.04 m² of steel was actually used Ans.