Pipes & Cistern

Important Instructions

81.

2/5 of a water tank is full. Pipe a fills the tank in 10 minutes, pipe B empties it in 6 minutes. Both the pipes if opened together, how long shall it take to fill or empty the entire tank?

A.6 min to empty
B.7 min to full
C.7 min to empty
D.6 min to full

Answer: A

There are two important points to learn in this type of question,
First, if both will open then tank will be empty first.

Second most important thing is,
If we are calculating filling of tank then we will subtract as (filling-empting)

If we are calculating empting of thank then we will subtract as (empting-filling)

So lets come on the question now,

Part to emptied 2/5

Part emptied in 1 minute =

1/6−1/10

=1/15

=>1/15:2/5 :: 1:x

=>2/5∗15

= 6mins

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82.

Three pipes A, B and C 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. A, B and C discharge chemical solutions P,Q and R respectively. What is the proportion of the solution R in the liquid in the tank after 3 minutes?

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

Answer: B

Part filled by (A + B + C) in 3 minutes = 3 (1/30 + 1/20 + 1/10) = (3 × 1/60) = 11/20

Part filled by C in 3 minutes = 3/10 .

Required ratio = (3/10 ×: 20/11) = 6/11

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83.

A tank has three taps P, Q and R. Taps P and Q can fill the tank in 1.5 and 2 hours, respectively. Tap R can empty the completely filled tank in just half hour. Tap P is opened at 8 am, tap Q is opened at 9am and tap R is opened at 10 am. At what exact time will the tank be empty?

A.12 pm
B.1.25 pm
C.12.12 pm
D.12.28 pm

Answer: C

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84.

Two pipes M and N can fill a tank in 22.5 and 15 minutes, respectively. If both the pipes are opened simultaneously, after how much time should N be closed so that the tank is full in 18 minutes?

A.4 minutes
B.3 minutes
C.4.5 minutes
D.2.5 minutes

Answer: B

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85.

A tap can completely fill a water tank in 8 hrs. The water tank has a hole in it through which the water leaks out. The leakage will cause the full water tank to get empty in 12 hrs. How much time will it take for the tap to fill the tank completely ..?

A.16 Hrs
B.18 Hrs
C.24 Hrs
D.28 Hrs

Answer: C

No answer description available for this question.

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86.

A pipe is 30 m long and is 45% longer than another pipe. Find the length of the other pipe.

A.20.68
B.20
C.20.12
D.20.5

Answer: A

Let length of other pipe be X
According to question,
30 = 45/100 X + X
30 = 0.45X + X
30 = 1.45 X
X= 30/1.45
X = 20.68m

Thus the length of the other pipe is 20.68 metres.

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87.

A 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 tank from empty state if B is used for the first half time and then A and B fill it together for the other half.

A.15 mins
B.20 mins
C.25 mins
D.30 mins

Answer: D

Let the total time be x mins.

Part filled in first half means in x/2 = 1/40

Part filled in second half means in x/2 =

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88.

Two pipes M and N can fill a tank in 22 hours and 33 hours respectively. In how much time will the tank be full, if both the pipes are opened simultaneously?

A.18 hours
B.19/22 hours
C.1(1/11) hours
D.13(1/5) hours

Answer: D

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89.

Two pipes A and B attached to a swimming pool can fill the pool in 20 minutes and 30 minutes respectively working alone. Both were opened together but due to malfunctioning of motor of pipe A, it had to be shut down after two minutes but B continued to work till the swimming pool was filled completely. Find the total time taken to fill the pool.

A.20
B.22
C.25
D.27

Answer: D

Let the capacity of the pool be LCM(20, 30) = 60 units.
=> Efficiency of pipe A = 60 / 20 = 3 units / minute
=> Efficiency of pipe B = 60 / 30 = 2 units / minute
=> Combined efficiency of pipe A and pipe B = 5 units / minute
Now, the pool is filled with the efficiency of 5 units / minute for two minutes.
=> Pool filled in two minutes = 10 units
=> Pool still empty = 60 – 10 = 50 units
This 50 units is filled by B alone.
=> Time required to fill these 50 units = 50 / 2 = 25 minutes

Therefore, total time required to fill the pool = 2 + 25 = 27 minutes