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A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining

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Bunuel
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A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 21:37
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A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5
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D
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uchihaitachi
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 22:06
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Bunuel wrote:
A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5


The pipe takes 3 hours to fill 2/7th of the tank.

Let us assume that the total capacity of the tank is LCM(3,7) = 21 liters.

Now the tank fills 2/7th of the tank in 3 hours i.e. it fills 6 liters in 3 hours.
So, it fills 2 liters in 1 hour.
From this we get the filling rate as 2 liters per hour.
So, the total time taken will be capacity/rate of filling = 21/2 = 10.5 hours.

IMO, Answer C is correct

If you like my solution, do give kudos!

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solikon
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 22:48
uchihaitachi wrote:
Bunuel wrote:
A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5


The pipe takes 3 hours to fill 2/7th of the tank.

Let us assume that the total capacity of the tank is LCM(3,7) = 21 liters.

Now the tank fills 2/7th of the tank in 3 hours i.e. it fills 6 liters in 3 hours.
So, it fills 2 liters in 1 hour.
From this we get the filling rate as 2 liters per hour.
So, the total time taken will be capacity/rate of filling = 21/2 = 10.5 hours.

IMO, Answer C is correct

If you like my solution, do give kudos!



Your approach is quite right but you did not answer to the question. The question asks for time till the tank is full. You have to subtract 3 hours from you result.

So Answer should be 7.5 hours
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 23:03
solikon wrote:
uchihaitachi wrote:
Bunuel wrote:
A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5


The pipe takes 3 hours to fill 2/7th of the tank.

Let us assume that the total capacity of the tank is LCM(3,7) = 21 liters.

Now the tank fills 2/7th of the tank in 3 hours i.e. it fills 6 liters in 3 hours.
So, it fills 2 liters in 1 hour.
From this we get the filling rate as 2 liters per hour.
So, the total time taken will be capacity/rate of filling = 21/2 = 10.5 hours.

IMO, Answer C is correct

If you like my solution, do give kudos!



Your approach is quite right but you did not answer to the question. The question asks for time till the tank is full. You have to subtract 3 hours from you result.

So Answer should be 7.5 hours


Thank you for pointing out the error. The total time is 10.5 hours.
The answer should be D then.
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 23:07
Bunuel wrote:
A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5



Since 2/7 has already been filled, we need to find the time taken to fill 5/7

2/7 is filled in 3 hours
So 1/7 is filled in 1.5 hours

This means 5/7 is filled in 1.5*5=7.5 hours

Answer is (D)

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tahen
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A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   12 Sep 2019, 23:18
Another approach:

2/7 is a fraction. So, consider the full capacity as 1.

2/7th of the tank in 3 hours
=> Full tank in 3 / (2/7) = 3 x (7/2) = 10.5 hours
So,
Remaining time 10.5 - 3 = 7.5 hours

Ans D
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink] New post   13 Sep 2019, 02:49
Bunuel wrote:
A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining (in hours) till the tank is completely filled?

A. 3
B. 3.5
C. 10.5
D. 7.5
E. 4.5


total capacity of tank 14 so filled tank ; 4
rate ; 4/3
left vol 10 ; time taken 10*3/4 ; 7.5 hrs
IMO D
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Re: A pipe takes 3 hours to fill 2/7 of a tank. What is the time remaining [#permalink]
13 Sep 2019, 02:49
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