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Akshita

· started a discussion

· 1 Months ago

sol (Question: 217526.0 )

Is there someone else who has an issue with this question?

Question:
Two pipes A and B can fill an empty tank in 12 hours and 15 hours respectively. while pipe C can empty the tank in 20 hours. If all the three pipes are opened, then after how much time the pipe A should be closed so that the tank be filled in 20 hours ?
Options:
A) 10 hours
B) 8 hours 
C) 6 hours
D) 5 hours
Solution:
Ans: (b)



Alternate sol.


A can fill the tank in 1 hour = 1/12

B can fill the tank in 1 hour = 1/15

C can empty the tank in 1 hour= 1/20


B and C can fill the tank in 1 hour= 1/15 - 1/20 = 1/60

B and C can Fill the tank in 20 hour= 1/60*20=1/3

Remaining part of the tank 1-1/3=2/3

 A takes X time to  fill the remaining part of the tank. 


1/12*(X) = 2/3

X = 8 hour. 


Knowledge Expert

· commented

· 1 Months ago

Dear Student,
Explanation,
A can fill the tank in 1 hour = 1/12
B can fill the tank in 1 hour = 1/15
C can empty the tank in 1 hour= 1/20

B and C can fill the tank in 1 hour = 1/15-1/20
= 1/60
B and C can fill the tank in 20 hour= 1/60*20= 1/3 part
remaining part = 1-1/3= 2/3
A can fill the tank in 1 hour = 1/12 part
time required to fill 2/3 part = (2/3)/(1/12)
= 8 hour.

I hope you got it,

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