Question

It takes 15 minutes to fill an oil tank. However the oil tank is being emptied through an exhaust pipe, which can empty it in 30 minutes. If this exhaust pipe remains open, how long will it take to fill this tank completely?

A. 20 minutes

B. 25 minutes

C. 30 minutes

D. 40 minutes

1. B
2. D
3. A
4. C

Answer 1

Correct Answer - Option 4 : C

Given :

Inlet pipe takes time to fill the tank = 15 minutes 

Outlet pipe takes to empty the tank = 30 minutes 

Formula Used: 

Work = Time × Efficiency 

Calculation: 

LCM of (15, 30) = 30 

Let be total work is 30 

Efficiency of Inlet pipe,

⇒ 30/15 = 2 

Efficiency of outlet pipe,

⇒ 30/30 = -1   (-ve indicate leakage)

Work done by both pipe are opened,

⇒ 30/(2 - 1) = 30 minutes 

∴ Both pipe together can fill the tank in 30 minutes