Aptitude - Pipes and Cistern
6.
A tap can fill a cistern in 8 hrs and another tap can empty it in 16 hrs. If both the taps are open, the time taken to fill the tank will be :
Answer
Part filled by both pipes in 1 min =
18 − 116 
= 116
Total time taken to fill the tank = 16 hrs.
Answer :
Option CExplanation :
Part filled by both pipes in 1 min =
18 − 116 = 116Total time taken to fill the tank = 16 hrs.
7.
Pipes A and B can fill a tank in 20 hrs and 30 hrs respectively and pipe C can empty the full tank in 40 hrs. If all the pipes are opened together how much time will be needed to make the tank full ?
Answer
Net part filled in 1 hr = 120 + 130 − 140 = 7120
Time needed to make the tank full = 1207 hrs = 1717 hrs.
Answer :
Option CExplanation :
Net part filled in 1 hr =
120 + 130 − 140 = 7120Time needed to make the tank full = 1207 hrs = 1717 hrs.
8.
A larger tank can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half ?
Answer
Let the total time taken be x minutes. Then,
140 x x2 + 160 + 140 x2 = 1
⇒ x80 + x48 = 1
⇒ 3x + 5x = 240 ⇒ 8x = 240 ⇒ x = 30
Hence, time required is 30 minutes.
Answer :
Option DExplanation :
Let the total time taken be x minutes. Then,
140 x x2 + 160 + 140 x2 = 1⇒ x80 + x48 = 1
⇒ 3x + 5x = 240 ⇒ 8x = 240 ⇒ x = 30
Hence, time required is 30 minutes.
9.
Two pipes A and B can fill a tank in 1 hr and 75 min respectively. There is also an outlet C. If all the three pipes are opened together, the tank is full in 50 minutes. How much time will be taken by C to empty the full tank ?
Answer
Work done by C in 1 min = 160 + 175 − 150 = 3300 = 1100
Hence, C can empty the full tank in 100 minutes.
Answer :
Option CExplanation :
Work done by C in 1 min =
160 + 175 − 150 = 3300 = 1100Hence, C can empty the full tank in 100 minutes.
10.
A pipe can fill a cistern in 12 minutes and another pipe can fill it in 15 minutes. But, a third pipe can empty it in 6 minutes. The first two pipes are kept open for 5 minutes in the begining and then the third pipe is also opened. In what time is the cistern emptied ?
Answer
Part filled in 5 min = 5 x 112 + 115 = 5 x 960 = 34
Part emptied in 1 min when all the pipes are opened
= 16 − 112 + 115 = 16 − 320 = 160
160 part emptied in 1 min.
34 part will be emptied in 60 x 34 min = 45 min.
Answer :
Option DExplanation :
Part filled in 5 min = 5 x
112 + 115 = 5 x 960 = 34Part emptied in 1 min when all the pipes are opened
= 16 −
112 + 115 = 16 − 320 = 160160 part emptied in 1 min.
34 part will be emptied in 60 x 34 min = 45 min.
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