Given: Time taken by first water tap to fill the empty tank = 12 hours Time taken by second water tap to fill the empty tank = 18 hours Time taken by leakage to empty the filled tank = 36 hours Formula used: Work = Efficiency × Time Calculation: LCM of 12, 18 and 36 is 36 Efficiency of first water tap = 36/12 = 3 units/hr Efficiency of second water tap = 36/18 = 2 units/hr Efficiency of leakage = 36/36 = 1 unit/hr Efficiency of these 2 taps and leakage together = (3 + 2 – 1) = 4 units/hr Remaining units = (36 – 4) = 32 units Work done by two tap water together to fill the empty tank = 32/(3 + 2) hr ⇒ 32/5 hr ⇒ 6.4 hours = 6 hours + 0.4 hours (0.4 hours = 24 minutes) ⇒ 6 hr 24 min Total time taken to fill the empty tank = (6 hr 24 min + 1 hr) ⇒ 7 hr 24 min ∴ The empty tank will completely filled in 7 hr 24 minutes Shortcut Trick[ alt="F3 Savita SSC 25-4-22 D3" src="//storage.googleapis.com/tb-img/production/22/04/F3__Savita_SSC_25-4-22_D3.png" style="width: 255px; height: 83px;"> For the first one hour = (3 + 2 - 1) × 1 = 4 units Time to fill remaning tank = (36 - 4) ÷ (3 + 2) = 6.4 hours Total time taken = (6.4 + 1) = 7.4 hours = 7 hr 24 min ∴ The empty tank will completely filled in 7 hr 24 minutes