# Aptitude Pipes and Cisterns Question and Answer

1) Three pipes X, Y and Z can fill a tank from empty to full in 30 minutes, 20 minutes, and 10 minutes respectively. When the tank is empty, all the three pipes are opened. X, Y and Z discharge chemical solutions A,B and C respectively. What is the proportion of the solution C in the liquid in the tank after 3 minutes?

A)
5 / 11
B)
6 / 11
C)
7 / 11
D)
8 / 11

6 / 11

Explanation:

Part filled by (X + Y + Z) in 3 minutes = 3(
1 / 30
+
1 / 20
+
1 / 10
) = ( 3 x
11 / 60
) =
11 / 20
Part filled by Z in 3 minutes =
3 / 10
Required ratio = (
3 / 10
x.
20 / 11
) =
6 / 11

2) A tap can fill a tank in 6 hours. After half the tank is filled then 3 more similar taps are opened. What will be total time taken to fill the tank completely.?
A) 2 hours 30 mins
B) 2 hours 45 mins
C) 3 hours 30 mins
D) 3 hours 45 mins

Explanation:

Half tank will be filled in 3 hours Lets calculate remaining half,

Part filled by the four taps in 1 hour = 4*(
1 / 6
) =
2 / 3
Remaining part after
1 / 2
filled = 1-
1 / 2
=
1 / 2
2 / 3
:
1 / 2
::1:X=>X=(
1 / 2*1*32
)=>X=3hrs 45mins

3) A water tank is two-fifth full. Pipe A can fill a tank in 12 minutes and pipe B can empty it in 6 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely?
A) 2.8 min
B) 4.2 min
C) 4.8 min
D) 5.6 min

Explanation:

Since pipe B is faster than pipe A, the tank will be emptied.
Part filled by pipe A in 1 minute =
1 / 12
Part emptied by pipe B in 1 minute =
1 / 6
Net part emptied by pipe A and B in 1 minute =Part filled by pipe A in 1 minute =
1 / 6
-
1 / 12
=
1 / 12
Time taken to empty
2 / 5
of the tank =
2 / 5
/
1 / 12
=
2 / 5
X 12 =4.8 min

4)Two pipes A and B can fill a cistern in 37
1 / 2
minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
?
A)5 min.
B)9 min.
C)10 min.
D)15 min.

Explanation:

Let B be turned off after x minutes. Then,
Part filled by (A + B) in x min. + Part filled by A in (30 -x) min. = 1.

x(
2 / 75
+
1 / 75
)+ (30 - x).
2 / 75
= 1
x (
11x / 225
+
(60 -2x) / 75
= 1 11x + 180 - 6x = 225.
x = 9.