# 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.

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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.

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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) m

= 44 × 0.3 × 6.6 m2 = 87.12 m

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 m

Hence, 95.04 m2 of steel was actually used Ans.

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