Aptitude Questions: Pipes & Cistern Set 2

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1. Two pipes A and B can fill a tank in 4 hours and 5 hours respectively. If they are opened on alternate hours and if pipe B is opened first, in how many hours, the tank fill in
   A.7hrs
   B.6hrs
   C.4.30hrs
   D.5hrs
   E.None of these
   
   Answer & Explanation

   Answer –C.4.30hrs
   Explanation :
   A+B = 1/4+1/5=9/20…………..2h
   A+B = 18/20………………………4h
   =9/10
   Remaining = 1-9/10 = 1/10…it take 1/2 hr=> B
   Already 4+ remaining 2(B) = 4+1/2 = 4.30hrs
   
   
   
2. A tap can fill a tank completely in 6 hours. After half the tank is filled , one more similar tap is opened. What is the total time taken to fill the tank completely ?
   A.4hrs 20min
   B.3hrs 30min
   C.3hrs 10min
   D.4hrs 30min
   E.None of these
   
   Answer & Explanation

   Answer – D. 4hrs 30min
   Explanation :
   Tab fill the half tank in 3hrs
   Now another similar tab opened
   1/6+1/6 = 2/6 = 1/3
   Remaining half tank filled in 1.5hrs
   Total time = 3+1.5 = 4hrs 30min
   
   
   
3. A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 7 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?
   A.9.00hrs
   B.9.20hrs
   C.9.30hrs
   D.9.33hrs
   E.None of these
   
   Answer & Explanation

   Answer – D. 9.33hrs
   Explanation :
   1/4 – 1/7 = 7-4/28
   Cistern filled in = 28/3 = 9.33hrs
   
   
   
4. A pipe can fill a tank in 5hours, but due to a leakage it took 7hours to fill the tank. If the tank is full, in what time will the tank become empty due to leakage ?
   A.15.30hrs
   B.17.50hrs
   C.16hrs
   D.12.30hrs
   E.None of these
   
   Answer & Explanation

   Answer – B.17.50hrs
   Explanation :
   1/5-1/7 = 7-5/35 = 2/35 = 1/17.5
   17.5hours
   
   
   
5. Two pipes A and B can separately fill a tank in 10 and 15 minutes respectively. A third pipe C can drain off 30 liters of water per minute. If all the pipes are opened, the tank can be filled in 10 minutes. What is the capacity of the tank?
   A.500litres
   B.370liters
   C.450liters
   D.320liters
   E.None of these
   
   Answer & Explanation

   Answer – C.450liters
   Explanation :
   1/10 + 1/15 – 1/x = 1/10
   x = 15
   15 * 30 = 450
   
   
   
6. Two pipes A and B can fill a tank in 20 min. and 40 min. respectively. A water pipe C can empty the tank in 20 min. First A and B are opened. After 7 min, C is also opened. In how much time, the tank is full?
   A.30m
   B.20m
   C.25m
   D.19m
   E.None of these
   
   Answer & Explanation

   Answer – D.19m
   Explanation :
   Part filled in 7 min. = 7*((1/20)+(1/40))=7(2+1/40) = 21/40
   Remaining part=(1-(21/40))=(19/40).
   Net part filled in 1min. when A,B and C are opened=(1/20)+(1/40)-(1/20)=(1/40).
   Now,(1/40) part is filled in one minute.
   (19/40) part is filled in = (40*(19/40))=19minutes.
   
   
   
7. An electric pump can fill a tank in 2 hours. Because of a leak in the tank, it took 2 hours 30 min to fill the tank. In what time the leak can drain out all the water of the tank and will make tank empty ?
   A.12hrs
   B.7hrs
   C.10hrs
   D.14hrs
   E.None of these
   
   Answer & Explanation

   Answer – C.10hrs
   Explanation :
   Work done for 1 hour without leak = 1/2
   Work done with leak = 2(1/2)=5/2
   Work done with leak in 1 hr= 2/5
   Work done by leak in 1 hr =1/2−2/5=5-4/10=1/10
   
   
   
8. Two pipes A and B can fill a cistern in 20 minutes and 30 minutes respectively. These pipes are opened alternately for 1 minute each, beginning with pipe A. In what time will the cistern be full?
   A.24minutes
   B.20minutes
   C.18minutes
   D.28minutes
   E.None of these
   
   Answer & Explanation

   Answer – A.24minutes
   Explanation :
   In 2 minutes the part of the cistern filled = [(1/20) + (1/30)]
   = (5/60) = (1/12)
   :.(1/12) part of cistern is filled in 2 minutes
   1 part of the cistern will be full in = (12×2) = 24 minutes
   
   
   
9. Two pipes P and Q fill a tank in 9hrs and 5hrs respectively.If both the pipes are opens together then after how many hours should Q closed so that the tank is full in 6hrs respectively ?
   A.8/3hrs
   B.5/3hrs
   C.5hrs
   D.3/2hrs
   E.None of these
   
   Answer & Explanation

   Answer – B.5/3hrs
   Explanation :
   Part of the tank is filled in 6hrs = 6/9 = 2/3
   Time taken by pipe Q = 5*1/3 = 5/3
   
   
   
10. A cistern has a leak which would empty the cistern in 10 minutes. A tap is turned on which admits 4 liters a minute into the cistern, and it is emptied in 15 minutes. How many liters does the cistern hold?
    A.120litres
    B.115litres
    C.110litres
    D.130litres
    E.None of these
    
    Answer & Explanation

    Answer – A.120litres
    Explanation :
    1/x – 1/10 = -1/15
    1/x = -1/15+1/10
    = -10+15/150 = 5/150
    1/x = 1/30
    X=30
    4x = 30*4 = 120litres
    
    
    

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