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Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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30 Nov 2010, 07:03
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Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity? A. 3.25 B. 3.6 C. 4.2 D. 4.4 E. 5.5
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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30 Nov 2010, 07:19
1/2 of capacity in 3 hours
full capacity in 6 hours
> pump A.
2/3 capacity in 6 hours
(2/3 +1/3) in 6+3 = 9 hours
> pump B
in 1 hour filled 1/6 +1/9 = 5/18 parts full in 18/5 hours 3.6 hrs.
HTH



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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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30 Nov 2010, 07:30
Inlet 1 fills x/6 in 1 hour inlet 2 fills (2x/3)/6 = x/9 in 1 hour so together in 1 hour they will fill x/6 + x/9 = 5x/18 which means to fill 5x/18 it takes 1 hour => to fill x it will take 18/5=3.6 hrs
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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01 Dec 2015, 02:51
rite2deepti wrote: Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?
A. 3.25 B. 3.6 C. 4.2 D. 4.4 E. 5.5 Assume the volume of the container to be 6 Lts We have assumed 6 because 6 is the LCM of 2 and 3, the denominators of the capacity filled.Inlet 1: 1/2 of capacity in 3 hours i.e. 3 lts in 3 hours Hence 1 lts/hour Inlet 2: 2/3 of capacity in 6 hours i.e. 4 lts in 6 hours Hence 2/3 lts/hour Inlet 1 + Inlet 2 combined rate = 6/(1 + 2/3) hours= 6/ (5/3) hours = 18/5 = 3.6 hours Option B



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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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01 Dec 2015, 13:04
rite2deepti wrote: one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours Time required to fill the full tank is 6 hours rite2deepti wrote: a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. Time required to fill the full tank is 9 hours rite2deepti wrote: How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity? Use the formula  \(\frac{AB}{(A + B)}\) Or, \(\frac{6*9}{(6 + 9)}\) Or, \(\frac{54}{15}\) Or, \(\frac{18}{5}\) Or, \(3.6\) Hence answer is (B) 3.6
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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10 May 2016, 18:21
Attached is a visual that should help.
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Screen Shot 20160510 at 5.50.37 PM.png [ 100.66 KiB  Viewed 8732 times ]
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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03 Jun 2017, 01:08
The first pipe fills the empty pool to half in 3 hours > meaning it will take the first pipe double the time, 6h to fill the whole pool. Now we have the rate of the first pipe: 1/6 The second pipe fills the pool to 2/3 in 6 hours. Multiply capacity and and time by 3/2 to obtain the rate it will take pipe 2 to fill to full capacity: 1/9 Now as we have two machines, two entities working together we can use the work formula: A*B/(A+B)= 6*9/(6+9) =54/15= 3.6 Answer B!



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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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04 Jun 2017, 15:59
Hi All, This question can be solved in a couple of different ways, but it's essentially just a Work Formula question. Work = (A)(B)/(A+B) where A and B are the respective times it takes for two entities to individually complete a task. To start, we have to figure out how long it takes each pipe to fill the FULL tank.... First pipe = fills 1/2 the tank in 3 hours... so it fills the FULL tank in 6 hours Second pipe = fills 2/3 the tank in 6 hours... so it fills the FULL tank in 9 hours Working together, the two pipes will fill the tank in (6)(9)/(6+9) = 54/15 = 3 9/15 hours = 3.6 hours Final Answer: GMAT assassins aren't born, they're made, Rich
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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14 Jul 2017, 23:18
Hi Sir, Could you please explain me your reasoning why you multiplied 2/3*6 hrs = 9 hrs. { Also why you did the reciprocal of 3/2*2/3 = 1} mcelroytutoring wrote: Attached is a visual that should help. Thank you



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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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08 Sep 2017, 01:03
Rate= Work/TimeLet total work = x Inlet pipe 1Time= 3 hours Work done= 1/2 *x Rate= x/2/3= x/6 Inlet pipe 2 Time= 6 hours Work done= 2/3 of x Rate= 2x/3/6 = x/9 Combined rate=x/6 + x/9= 5x/18 Again the same formula: Rate= Work/Time 5x/18= x/Time Time= x/5x/18= 18/5= 3.6 Another method is to consider the total work as the LCM (2,3) (Denominators) Total work= 6 Inlet pipe 1 Time= 3 Work done= 1/2 *6= 3 Rate= 3/3= 1 Inlet pipe 2 Time= 6 Work done= 2/3 * 6= 4 Rate= 4/6= 2/3 Combined rate= 1+2/3= 5/3 Work= 6 Time= 6/5/3= 18/5= 3.6
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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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10 Sep 2017, 20:54
rite2deepti wrote: Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?
A. 3.25 B. 3.6 C. 4.2 D. 4.4 E. 5.5 1st pipe fills 1/6 cap in 1 hr. 2nd pipe fills 1/9 cap in 1hr Together 1/6+1/9 = 5/18 in 1 hr. Full capacity in 18/5 hrs i.e 3.6 hrs. Ans:B



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Re: Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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11 Sep 2017, 16:02
rite2deepti wrote: Pumping alone at their respective constant rates, one inlet pipe fills an empty tank to 1/2 of capacity in 3 hours and a second inlet pipe fills the same empty tank to 2/3 of capacity in 6 hours. How many hours will it take both pipes, pumping simultaneously at their respective constant rates, to fill the empty tank to capacity?
A. 3.25 B. 3.6 C. 4.2 D. 4.4 E. 5.5 The rate for the first inlet pipe is (1/2)/3 = 1/6 and the rate for the second pipe is (2/3)/6 = 2/18 = 1/9. If we let t = the number of hours they work together to fill the empty tank, we have: (1/6)t + (1/9)t = 1 t/6 + t/9 = 1 Multiplying the entire equation by 18, we have: 3t + 2t = 18 5t = 18 t = 18/5 = 3 ⅗ = 3.6 Answer: B
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Pumping alone at their respective constant rates, one inlet pipe fills [#permalink]
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24 Jan 2018, 00:23
I have a rather random question for dabral and Bunuel: why can't we use the harmonic mean (average of rates) formula here? Is it sheer coincidence that the answer I am getting (3.75) with this equation is so close to the actual answer (3.6)? 1st pipe rate = 1/6 tank per hour 2nd pipe rate = 1/9 tank per hour Harmonic mean (average of rates) = #/sum of inverse of rates = 2 / (6 + 9) = (2/15) x 2 = 4/15 per hour. (4/15)x = 1, x = 15/4 = 3.75 Yet the answer is 3.6 with the more traditional (and admittedly easy and straightforward) method. Still, what am I doing wrong? Thanks!
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Pumping alone at their respective constant rates, one inlet pipe fills
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