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1. Three taps A, B and C can fill a tank in 12,25 and 20 hours respectively. If a is open all the time and B and C are open for one hour each alternately, the tank will be full in :

  • A. 7 hrs
  • B. 7 hrs
  • C. 7 hrs
  • D. 7 hrs

Answer: Option A

Explanation:

Hints: Answer not given.

A + B s 1 hour work = ( 1/12 + 1/15) = 3/20

A + C s hours work = ( 1/12 + 1/20) = 2/15

Part filled in 2 hrs = ( 3/20 + 2/15) = 17/60

part filled 6 hrs = (3× 17/60) = 17/20

Remaining part = ( 1 - 17/20) = 3/20

Now, it is the turn of A and B and 3/20 part is filled by A and B in 1 hour

Total time taken to fill the tank = ( 6 + 1) = 7 hrs

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