Question

There are 1 inlet & 1 outlet pipes and ratio of their efficiency is 2 ∶ 1. If inlet pipe fills the tank in 12 hours, then in how many hours both the pipes will fill the tank? 
1. 12
2. 24
3. 36
4. 18

Answer 1

Correct Answer - Option 2 : 24

Given:

Ratio of efficiency of inlet pipe to outlet pipe is 2 ∶ 1.

Inlet pipe fills the tank in 12 hours.

Concept used:

Total capacity = LCM of time

Efficiency = (Total capacity)/(Total time)

Calculations:

Let the efficiency of inlet pipe & outlet pipe be '2x' & '1x'.

Total capacity of tank = (Efficiency of inlet pipe) × (Time taken to fill the tank)

⇒ (2x) × 12

⇒ 24x

Time taken to fill the tank by working together 

⇒ (Capacity of the tank)/(Combined efficiency)

⇒ (24x)/(2x - 1x)

⇒ 24

∴ The time taken by both the pipes is 24 hours.