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.

`["Assume "pi=22/7]`

#### Solution

Height (*h*) of cylindrical tank = 4.5 m

Radius (*r*) of the circular end of cylindrical tank = (4.2/2)m = 2.1m

(i) Lateral or curved surface area of tank = 2π*rh*

`=(2xx22/7xx2.1xx4.5)m^2`

= (44 × 0.3 × 4.5) m^{2}

= 59.4 m^{2}

Therefore, CSA of tank is 59.4 m^{2}.

(ii) Total surface area of tank = 2π*r *(*r + h*)

`=[2xx22/7xx(2.1+4.5)]m^2`

= (44 × 0.3 × 6.6) m^{2}

= 87.12 m^{2}

Let A m^{2} steel sheet be actually used in making the tank.

`therefore(1-1/12)=87.12m^2`

`rArr A=(12/11xx87.12)m^2`

⇒ A = 95.04 m^{2}

Therefore, 95.04 m^{2} steel was used in actual while making such a tank.