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Arithmetic Ability
Pipes and Cistern

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Q.

Three taps A,B and C can fill a tank in 12,15 and 20 hours respectively. If A is open all the time and B ,C are open for one hour each alternatively, the tank will be full in:

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Correct choice: C

Explanation:

(A+B)'s 1 hour work=( 1 12 + 1 15 )= 9 60 = 3 20 A+B's 1 hour work=112+115=960=320 (A+C)'s 1 hour work=( 1 12 + 1 20 )= 8 60 = 2 15 A+C's 1 hour work=112+120=860=215 part filled in 2 hrs=( 3 20 + 2 15 )= 17 60 part filled in 2 hrs=320+215=1760 part filled in 6 hrs=(3* 17 60 )= 17 20 part filled in 6 hrs=3*1760=1720  remaining part =(1− 17 20 )= 3 20 remaining part =1-1720=320 Now, it is  the turn of A and B (3/20) part is filled by A and B in 1 hour. Therefore, Total  time taken to fill the tank =(6+1)hrs= 7 hrs
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