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Q:

Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?

A) 10 min. 20 sec. B) 11 min. 45 sec.
C) 12 min. 30 sec. D) 14 min. 40 sec.

Answer:   D) 14 min. 40 sec.

Explanation:

Part filled in 4 minutes ={\color{Black} 4\left ( \frac{1}{15}+\frac{1}{20} \right )=\frac{7}{15}}

Remaining part ={\color{Blue} \left ( 1-\frac{7}{15} \right )=\frac{8}{15}}

Part filled by B in 1 minute ={\color{Black} \frac{1}{20}}

{\color{Black}\therefore \frac{1}{20}:\frac{8}{15}::1:x}

{\color{Black}x=\left ( \frac{8}{15} \times 1\times 20\right )=10\frac{2}{3}min=10min.40sec.}

{\color{Black} \therefore }The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec

Q:

A tank is filled in eight hours by three pipes K, L and M. Pipe K is twice as fast as pipe L, and L is twice as fast as M. How much time will pipe L alone take to fill the tank ?

A) 32 hrs B) 24 hrs
C) 28 hrs D) 26 hrs
 
Answer & Explanation Answer: C) 28 hrs

Explanation:

1/K + 1/L + 1/M = 1/8 (Given)
Also given that K = 2L and L = 2M
=> 1/2L + 1/L + 2/L = 1/8
=> (1 + 2 + 4)/2L = 1/8
=> 2L/7 = 8
=> L = 28 hours.

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1 13
Q:

Two pipes A and B can fill a tank in 15 min and 20 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank ?

A) 15 min 20 sec. B) 16 min 40 sec.
C) 13 min 10 sec. D) 14 min 40 sec.
 
Answer & Explanation Answer: D) 14 min 40 sec.

Explanation:

Part filled in 4 minutes = 4(1/15 + 1/20) = 7/15

Remaining part = 1 - 7/15 = 8/15

Part filled by B in 1 minute = 1/20

1/20 : 8/15 :: 1 : k

k = 8/15 x 1 x 20 = 10 2/3 min = 10 min 40 sec.

The tank will be full in (4 min. + 10 min. 40 sec) = 14 min 40 sec.

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3 58
Q:

Two pipes A and B can separately fill a cistern in 10 and 15 minutes respectively. A person opens both the pipes together when the cistern should have been was full he finds the waste pipe open. He then closes the waste pipe and in another 3 minutes the cistern was full. In what time can the waste pipe empty the cistern when fill  ?

A) 8.21 min B) 8 min
C) 8.57 min D) 8.49 min
 
Answer & Explanation Answer: C) 8.57 min

Explanation:

1/10 + 1/15 = 1/6 x 3 = 1/2

1 - 1/2 = 1/2

1/10 + 1/15 - 1/x = 1/2

x = 8.57 min

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1 33
Q:

Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes  ?

A) 21 min B) 24 min
C) 20 min D) 22 min
 
Answer & Explanation Answer: A) 21 min

Explanation:

Let the pipe B be closed after 'K' minutes.

30/16 - K/24 = 1 => K/24 = 30/16 - 1 = 14/16

=> K = 14/16 x 24 = 21 min.

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1 23
Q:

A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in    ?

A) 20 hrs B) 28 hrs
C) 36 hrs D) 40 hrs
 
Answer & Explanation Answer: A) 20 hrs

Explanation:

1/8 - 1/x = 1/10

x = 40 hrs

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