Quantitative Aptitude Questions and Answers - Pipes and Cistern
11. Taps P, Q and R can fill a tank in 3, 4 and 5 hours respectively. If all the taps are opened together and
after 30 minutes taps Q and R are turned off, find the total time in which the tank is full.
Explanation: In 1 hr P, Q, R = 1/3+1/4+1/5 = 20+15+12/60 = 47/60
Filled in 30m = 47/120
Remaining = 1-47/120 =73/120
Tap P = 3*73/120= 219/120
Total = 219/120+1/2 =219+60 /120= 279/120 hrs
12. Three tubes A, B and C can fill a tank in 12hours. After working at it together for 4 hours, C is closed and
A and B can fill the remaining part in 12 hours. The number of hours taken by C alone to fill the tank is
Explanation: A+B+C in 1h = 1/12
A+B+C in 4h = 4/12 = 1/3
Remaining = 1-1/3 = 2/3
A+B in 12hrs = 2/3
A+B in 1hr = 2/36=1/18
C alone to fill the tank= 1/12– 1/18 = 3-2/36= 1/36=36hrs
13. A Bunker has a leak which would empty the completely filled bunker in 20 hours. If the bunker is full of
water and a tap is opened which admits 4 litres of water per minutes in the bunker, how many litres does the
Explanation: Leak emptied the bunker per hour = 100/20 = 5% of water per hour;
Quantity of water emptied per hour = 4*60 = 240;
Thus, 5% = 240 liter;
Hence, capacity of water,
100% = 240*100/5= 4800 liter
14. One tube can fill a tank five times as fast as another tube. If together the two tubes can fill tank in 42 min,
then the slower tube alone will be able to fill the tank in?
Explanation: Let the slower tube alone fill the tank in x min.
Then, faster tube will fill it in x/5 min.
1/x + 5/x = 1/42
6/x = 1/42
=> x = 252min
15. A cistern is filled in 15 hours by three pipes P, Q and R. The pipe R is thrice as fast as Q and Q is thrice
as fast as P. How much time will pipe P alone take to fill the tank?
Explanation: Suppose pipe P alone takes x hours to fill the tank.
Then, pipes Q and R will take x/3 and x/9hours respectively to fill the tank.
1/x + 3/x + 9/x = 1/15
13/x = 1/15
=> x = 195 hrs.
16. Three pumps, M, N and O are opened to fill a tank such that M and N can fill the tank alone in 18 min. and
23 min. respectively and O can empty it in 15 min. After 3 minutes the emptying pipe is closed. In how many
minutes the tank will be full in this way?
Explanation: Let the tank full in x minutes, then M and N opened for x minutes and O for 3 minutes.
(1/18 + 1/23)*x – (1/15)*3 = 1
Solve, x = 12
17. Two faucet A and B can fill a tank in 20 hours and 40 hours respectively. If they are opened
simultaneously. Sometimes later, tap B was closed, then it takes total 14 hours to fill up the whole tank. After
how many hours B was closed?
Explanation: Let x is the time when B is closed
18. A tap can fill a bunker in 4 hours. After half the bunker is filled, three more similar tap are opened. What is
the total time taken to fill the bunker completely?
Explanation: In One hour tap can fill = 1/4
Time is taken to fill half of the bunker = 1/2 * 4= 2hours
Part filled by four taps in one hour = (4*1/4) = 1
Required Remaining Part = 1/2
Total time = 2+ 1 /2=2.5 hrs
19. 24 tins of water fill a bunker when the capacity of each bunker is 27litres. How many tins will be needed to
fill the same bunker, if the capacity of each tin is 18litres?
Explanation: Capacity of the bunker = (24 * 27)litres
Capacity of each tin = 18litres
Number of tins needed = 648/18
20. Bucket A has twice the capacity as bucket B. It takes 120 turns for bucket A to fill the empty dumper. How
many turns it will take for both the buckets A and B, having each turn together to fill the empty dumper.
Explanation: Let capacity of A be x litres
Then capacity of B = x/2 litres
Capacity of the dumper = 120x litres
Required number of turns = 120x/ x =x/2
= 2 (120x)/3x