Correct Answer - Option 4 : 24 hrs
Given:
The first tap can fill the cistern in 6 hrs
The second tap can empty the tank in 8 hrs
Concept used:
Time ∝ 1/Efficiency
Calculation:
Taking the L.C.M of 6 and 8
L.C.M of 6 and 8 = 24
⇒ Efficiency of first tap = 24/6 = 4
⇒ Efficiency of second tap = 24/8 = 3
1-hour work when both taps are opened = 4 - 3 = 1
Both taps will fill the tank in 24/1 = 24 hrs
∴ The required time is 24 hours.