Question

Find

1)the lateral surface area of a closed cylindrical petrol storage tank that is 4.2m in diameter and 4.5m high.

2)howuch 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.