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03 Dec 2020, 01:15
Kudos
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
80% (02:05) correct
20%
(02:56)
wrong
based on 128
sessions
History
Date
Time
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Not Attempted Yet
Pipes A and B can fill a tank in 12 min and 16 min respectively. Both are kept open for 'n' min and then B is closed and A fills the rest of the tank in 5 min. The time 'n' after which B was closed is:
A. 2 min
B. 3 min
C. 4 min
D. 5 min
E. 6 min
A. 2 min
B. 3 min
C. 4 min
D. 5 min
E. 6 min
chinmayektare
Joined: 28 Nov 2018
Last visit: 18 Feb 2024
Posts: 122
Given Kudos: 34
Location: India
Concentration: General Management, Leadership
Schools: Tepper '24 (D)
GPA: 4
03 Dec 2020, 22:38
Kudos
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Bunuel
The answer should be C.4 min
Time taken for A and B is 12 min and 16 min respectively.
Taking LCM we get 48.
Le us assume there are 48 units to be filled.
Hence rate of filling for A would be 48/12 = 4 units per minute.
Similarly for B it would be 48/16 = 3 units per minute.
Now the time they are filling together is 'n' minutes. Hence combined rate of work during time 'n' is 4+3 = 7 minutes.
Using work done = rate * time taken we get,
work done = 7*n
After that , B is stopped and A fills the tap in 5 min
so work done by A is 4*5=20 units.
Hence , Total work done = combined work done + work done by A
i.e, 48=7*n +20 ==> n=4
Hence after 4 minutes B was closed.
04 Dec 2020, 02:37
Kudos
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Bunuel
Total Work = 48
Efficiency(A) = 48/12= 4
Efficiency(B) = 48/16 = 3
Efficiency(A+B) = 4+3 = 7
7n + 4(5) = 48
n = 4
C
