Question

Two pipes 'L' and 'K' together fill a tank in 4 hours. Pipe K alone fills it in 5 hours. In how many hours will pipe L fill this tank alone?
1. 20 hours
2. 12 hours
3. 8 hours
4. 15 hours

Answer 1

Correct Answer - Option 1 : 20 hours

Given:

Time taken by (L + K) to fill the tank = 4 hours

Time taken by K to fill the tank = 5 hours

Formula Used:

Efficiency = Total work/Time taken

Calculation:

LCM of 4 and 5 = 20 = Total work

Efficiency of L and K = 20/4 units/day

⇒ 5 units/day

Efficiency of K = 20/5 units/day

⇒ 4 units/day

Efficiency of L = (5 – 4) = 1 unit/day

Time taken by pipe L = 20/1 hours

⇒ 20 hours

∴ Time taken by pipe L alone is 20 hours