Question

One inlet and outlet pipe attached with a empty tank of internal depth 60m. First inlet pipe is opened for 1 minute increases the water level by 5m but when outlet pipe is opened for next 1 minute it decreases the water level by 4m. If both piped are opened alternatively in the same manner, in how much time the tank will be completely filled ?

1. 120 min
2. 60 min
3. 112 min
4. 111 min

Answer 1

Correct Answer - Option 4 : 111 min

Given:

Increase in the level of water by inlet pipe in 1 min = 5m 

decrease in the level of water by outlet pipe in 1 min = 4m 

Formula used: 

Time = work/efficiency 

Calculation:

Increase in the level in first 2 minutes = +5 - 4 = 1m 

⇒ Increase in the level in 110 minutes = 55m

⇒ Increase in the level in 111 minutes = 55 + 5 = 60m

∴ The whole tank will be filled in 111 minutes.