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Bunuel
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Bunuel
When Jacob closes the drain of his bathtub and turns on the cold water spigot, it takes him 3 minutes and 40 seconds to fill the tub completely. If he fills it from the hot water spigot instead, it takes him 5 minutes and 30 seconds to fill it completely. When the drain is open in a completely full bath tub, it takes 11 minutes for the tub to empty. How many minutes will it take Jacob to fill the bathtub with both hot and cold water running simultaneously, if the drain is open and draining at a constant pace ?

A. 2 minutes 12 seconds
B. 2 minutes 45 seconds
C. 3 minutes 30 seconds
D. 3 minutes 52 seconds
E. 4 minutes 15 seconds


­
Cold water CW takes 3 min 40 sec = 220 seconds.
Hot Water HW takes 5 min 30 sec = 330 seconds.

Drain pipe takes 11 mins = 660 seconds to empty the bath tub.

Total work = LCM of 220, 330, 660 = 660 units.

Rate of CW = 660/220 = 3
Rate of HW = 660/330 = 2

Rate of Drain = 660/660 = 1 (-ve )

All working simultaneously = 3+2-1 = 4

Total time taken by all three pipes (CW + HW - Drain) = 660/4 = 165 seconds.

165 seconds = 120 + 45 = 2 hrs 45 minutes.

Option B
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Method: Using Efficiency

  • Pipe \(A\)(inlet), takes \(3\) m \(40\) sec (Convert this time to seconds) \(= 3\times 60 + 40 = 220\) sec

  • Pipe \(B\)(inlet), takes \(5\) m \(30\) sec \(= 5\times 60 + 30 = 330\) sec

  • Pipe \(C\)(outlet), takes \(11\) m \(= 11\times 60 = 660\) sec

To find the efficiency of pipes A, B, and C, we calculate the LCM of their times in seconds—the total work i.e. \(LCM(220, 330, 660) = 660\)

The efficiencies are determined by dividing the total work by the individual times:

  • Efficiency of \(A = \dfrac{660}{220} = +3\) (inlet)

  • Efficiency of \(B = \dfrac{660}{330} = +2\) (inlet)

  • Efficiency of \(C = \dfrac{660}{660} = -1\) (Outlet)

When pipes A, B, and C are open together, the total work is completed in \( \dfrac{660}{3+2-1} = 165\) sec = \(2\) min \(45\) sec

ANS B
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