# Quantitative Aptitude Pipes and Cistern

Q1. Two pipes A and B can fill a tank in 10 and 40
minutes respectively. If both the pipes starts together,
then how long will it takes to fill the tank ?

(a) 6 minutes

(b) 8 minutes

(c) 12 minutes

(d) 15 minutes

**Answer:** (b) 8 minutes

Part filled by A in 1 min = 1/10

Part filled by B in 1 min = 1/40

Parts filled by (A + B) in 1 min = (1/10 + 1/40) = 1/8

So (A + B) can fill the tank in 8 minutes

Q2. Two pipes A and B can fill a tank in 2 hrs and 4 hrs respectively.
Another piper C can empty the tank in 12 hrs. If all the
three pipes open together, then how much time will be taken
to fill the tank ?

(a) 45 minutes

(b) 50 minutes

(c) 1 1/2 hours

(d) 2 1/2 hours

**Answer:** (c) 1 1/2 hours

Part filled 1 hr = (1/2 + 1/4 - 1/12) = 2/3

So the tank can be filled in 3/2 hrs =1 1/2 hours

Q3. A pipe can fill a tank in 4 hours. Beacause of a
leak, it took 6 hours to fill the tank completely. How much
time will the leak take to empty the tank ?

(a) 12 hours

(b) 10 hours

(c) 7 hours

(d) 5 hours

**Answer:** (a) 12 hours

Work done by the leak in 1 hour = 1/4 - 1/6 = 1/12

So the tank can empty the tank in 12 hours

Q4. One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in

(a) 81 minutes

(b) 108 minutes

(c) 144 minutes

(d) 192 minutes

**Answer:** (c) 144 minutes

Let the slower pipe can alone fill the tank in x minutes

Then fater pipe can fill it in x/3 minutes

1/x + 3/x = 1/36

4/x = 1/36

x = 144

So the slower pipe can fill the tank in 144 minutes

Q5. Two pipes A and B can fill a tank in 12 minutes and 15 minutes respectively. If both the taps are opened simultaneously and the tap A is closed after 3 minutes, then how much more time will it take to fill the tank by tap B

(a) 7 min 15 sec

(b) 7 min 45 sec

(c) 8 min 5 sec

(d) 8 min 15 sec

**Answer:** (d) 8 min 15 sec

Part filled in 3 minutes = 3(1/12 + 1/15)= 9/20

So Remaining Part =(1 - 9/20)= 11/20

Part filled by B in 1 minute = 1/20

1/15 : 11/20 :: 1 : x

or x = (11/20 X 1 X 5) = 8(1/4)

So the remaining part is filled by B in 8 min 15 sec

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