Author 
Message 
TAGS:

Hide Tags

Manager
Joined: 04 Aug 2013
Posts: 102
Location: India
GPA: 3
WE: Manufacturing and Production (Pharmaceuticals and Biotech)

A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
Updated on: 03 Jun 2016, 20:26
7
This post was BOOKMARKED
Question Stats:
72% (02:11) correct 28% (03:21) wrong based on 111 sessions
HideShow timer Statistics
A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ? A. 8640 B. 8740 C. 8840 D. 8540 E. 8940
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by anceer on 03 Jun 2016, 20:19.
Last edited by anceer on 03 Jun 2016, 20:26, edited 1 time in total.



Math Expert
Joined: 02 Aug 2009
Posts: 5769

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
03 Jun 2016, 20:22
anceer wrote: 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 Your Q is incomplete..... Please repost with full details
_________________
Absolute modulus :http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
GMAT online Tutor



Math Expert
Joined: 02 Aug 2009
Posts: 5769

A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
03 Jun 2016, 20:51
anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 Yes, now the Q is complete.. Lets find 1hour work1hr work of leakage = 1/8... 1hr work of both combined = 1/12... so 1hour wk of tap =\(\frac{1}{8}  \frac{1}{12} = \frac{32}{24} = \frac{1}{24}..\) so TAP will take 24 hr to fill the cistern.. speed of tap = 6 ltrs per minute = 6*60 = 360 ltrs per hour..Capacity = 360*24 = 8640.. A
_________________
Absolute modulus :http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
GMAT online Tutor



Senior Manager
Joined: 18 Jan 2010
Posts: 256

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
03 Jun 2016, 21:05
anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 Suppose the volume of cistern is V. Leak can be considered as a negative tap. The outflow through the leak is (V/8) Litres per hour. Incoming water is: 6 Ltrs per minute = 6 *60 litres per hour = 360 Litres per hour Total Volume that is emptied = V \(\frac{V}{([m][fraction]V/8}\))  360[/fraction][/m] = 12 hours V = \(\frac{12 V}{8}\)  360 *12 \(\frac{4 V}{8}\) = 360 *12 V = 360 * 12 * 2 = 8640 Litres



Manager
Joined: 16 Mar 2016
Posts: 131
Location: France
GPA: 3.25

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 05:23
Incoming water = + 6 l/min = 360 l/h Outcoming water =  X/8 l/h, X being the cistern's volume.
So, (360  X/8)*12 = x x=1728
Why is it false ?



Math Expert
Joined: 02 Aug 2009
Posts: 5769

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 05:31
Alex75PAris wrote: Incoming water = + 6 l/min = 360 l/h Outcoming water =  X/8 l/h, X being the cistern's volume.
So, (360  X/8)*12 = x x=1728
Why is it false ? hi, it is false because the equation is not correct..... which is more  INCOMING or OUTGOING? Outgoing as the cistern gets emptied when BOTH are switched on..so equation is.. \(( \frac{X}{8}360)*12 = x...............\frac{3x}{2}4320 = x...........................\frac{x}{2}=4320..................x = 8640\) hope it helps
_________________
Absolute modulus :http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
GMAT online Tutor



Current Student
Joined: 18 Oct 2014
Posts: 886
Location: United States
GPA: 3.98

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 08:24
anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 chetan2u, kindly suggest if below method is correct. Inflow of water in 12hrs with rate 6 lit/min= 6*60*12= 4320 But, the same volume is emptied in 12 hrs, so the total capacity = total inflow + total outflow= 4320+4320= 8640
_________________
I welcome critical analysis of my post!! That will help me reach 700+



Math Expert
Joined: 02 Aug 2009
Posts: 5769

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 08:37
Divyadisha wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 chetan2u, kindly suggest if below method is correct. Inflow of water in 12hrs with rate 6 lit/min= 6*60*12= 4320 But, the same volume is emptied in 12 hrs, so the total capacity = total inflow + total outflow= 4320+4320= 8640 Hi, May not be correct for two reasons 1) This would mean the answer will remain same irrespective of the speed of leakage, but it is dependent on BOTH leakage and inflow.. 2) Quote: the same volume is emptied in 12 hrs No the volume that is emptied in 12 hrs is INFLOW + CAPACITY..... May be the answer has matched here because the time taken to fill up tank is found 24 hours, double of 12hours
_________________
Absolute modulus :http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
GMAT online Tutor



Current Student
Joined: 18 Oct 2014
Posts: 886
Location: United States
GPA: 3.98

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 08:44
chetan2u wrote: Divyadisha wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 chetan2u, kindly suggest if below method is correct. Inflow of water in 12hrs with rate 6 lit/min= 6*60*12= 4320 But, the same volume is emptied in 12 hrs, so the total capacity = total inflow + total outflow= 4320+4320= 8640 Hi, May not be correct for two reasons 1) This would mean the answer will remain same irrespective of the speed of leakage, but it is dependent on BOTH leakage and inflow.. 2) Quote: the same volume is emptied in 12 hrs No the volume that is emptied in 12 hrs is INFLOW + CAPACITY..... May be the answer has matched here because the time taken to fill up tank is found 24 hours, double of 12hours Thanks chetan2u. I understood now. Initial rate Rate of inflow= Final rate x/8 360= x/12
_________________
I welcome critical analysis of my post!! That will help me reach 700+



Math Expert
Joined: 02 Aug 2009
Posts: 5769

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 08:46
Divyadisha wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 chetan2u, kindly suggest if below method is correct. Inflow of water in 12hrs with rate 6 lit/min= 6*60*12= 4320 But, the same volume is emptied in 12 hrs, so the total capacity = total inflow + total outflow= 4320+4320= 8640 Hi, But if you want to work on the method that you have applied.. the water filled up initially in tank is emptied in 8 hours but now it takes 12 hours to remove the water filled up initially and also the water being filled up by the tap.. so the water filled up by the tap is being removed in 4 hours, as you have found the water filled up is 4320... so leakage removes 4320 in 4 hours and therefore the capacity is WHAT it removes in 8 hours = 4320 *2 = 8640..
_________________
Absolute modulus :http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
GMAT online Tutor



Current Student
Joined: 18 Oct 2014
Posts: 886
Location: United States
GPA: 3.98

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
04 Jun 2016, 08:52
chetan2u wrote: Divyadisha wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 chetan2u, kindly suggest if below method is correct. Inflow of water in 12hrs with rate 6 lit/min= 6*60*12= 4320 But, the same volume is emptied in 12 hrs, so the total capacity = total inflow + total outflow= 4320+4320= 8640 Hi, But if you want to work on the method that you have applied.. the water filled up initially in tank is emptied in 8 hours but now it takes 12 hours to remove the water filled up initially and also the water being filled up by the tap.. so the water filled up by the tap is being removed in 4 hours, as you have found the water filled up is 4320... so leakage removes 4320 in 4 hours and therefore the capacity is WHAT it removes in 8 hours = 4320 *2 = 8640.. Awesome! That's exactly what I was looking for. You are awesome!!
_________________
I welcome critical analysis of my post!! That will help me reach 700+



Intern
Joined: 26 May 2016
Posts: 22

A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
07 Dec 2016, 04:46
Can someone explain if this is correct:
Total volume = V Cistern is emptied in 8 hours, say the rate of leakage is x Given that the rate of tap filling the water is 6 liter/min or 6*60 = 360 liter / hour Now, with both the leakage and the tap water, the cistern is emptied in 12 hours.
So, V=8x and V = 12(360+x)
combining:
8x = 12(360+x) =>4x=3(360+x) =>4x=3*360+3x =>x=3*360
and V= 8x = 8*3*360 = 8640



Director
Joined: 07 Dec 2014
Posts: 961

A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
11 Dec 2016, 13:56
anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 if leak empties 1 cistern in 8 hours, then it will empty 1 1/2 cisterns in 12 hours but with tap running, it only empties 1 thus, tap fills 1/2 of cistern in 12 hours 12 hours*360 lph=4320 liters 4320/(1/2)=8640 liters A



Intern
Joined: 03 Jun 2013
Posts: 1
Concentration: Entrepreneurship, Marketing
GMAT Date: 08092013

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
11 Dec 2016, 18:17
gracie wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 if leak empties 1 cistern in 8 hours, then it will empty 1 1/2 cisterns in 12 hours but with tap running, it only empties 1 thus, tap fills 1/2 of cistern in 12 hours 12 hours*360 lph=4320 liters 4320/(1/2)=8640 liters A Could you help me understand why you got 4320, but then divided by half? Thanks!



Senior Manager
Joined: 21 Aug 2016
Posts: 294
Location: India
GPA: 3.9
WE: Information Technology (Computer Software)

A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
11 Dec 2016, 23:46
nbestman wrote: gracie wrote: anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 if leak empties 1 cistern in 8 hours, then it will empty 1 1/2 cisterns in 12 hours but with tap running, it only empties 1 thus, tap fills 1/2 of cistern in 12 hours 12 hours*360 lph=4320 liters 4320/(1/2)=8640 liters A Could you help me understand why you got 4320, but then divided by half? Thanks! Hi nbestman Initially, the question says that the leak can empty the cistern in 8 hours, but when the tap which fills the cistern at certain rate is opened, the cistern get empty in 12 hours. (That means leaking lts/hr are more than filling lt/hr) If there would not be any tab to fill the cistern, the leak would have emptied 1 1/2(3/2) cisterns in 12 hours (as it empty 1 cistern in 8 hours) but with the tab running, it only empties 1. that means tab must have filled 1/2 cistern in 12 hours. If half cistern can be filled in 12 hours by the tab then full cistern will be filled in 24 hours by the tab we have to find out the capacity of the cistern. As we know that, in one min, tab fills 6 lts; in 24 hours(24*60 mins), tab will fill 6*24*60= 8640 lts (Gracie calculated the capacity of half cistern first and multiplied it by 2).If you find it difficult to approach the question in this way, here is another way Another approach :Let's say that the tab fills the cistern in x hours and we know that leak empty the cistern in 8 hours. We also know when both are open, it get empty in 12 hours 1/81/x=1/12 (why not 1/x 1/8=1/12 because cistern get empty ) x=24 we have to find out the capacity of the cistern. As we know that, in one min, tab fills 6 lts; in 24 hours(24*60 mins), tab will fill 6*24*60= 8640 lts Hope it helps.. Please press +1 Kudos if you like the post



Senior Manager
Status: Countdown Begins...
Joined: 03 Jul 2016
Posts: 304
Location: India
Concentration: Technology, Strategy
GPA: 3.7
WE: Information Technology (Consulting)

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
12 Dec 2016, 06:17
Simple work rate approach: Let the total capacity be x. Rate of leak  x/8 Rate after opening tap  x/8  360 > 1min  6litres so 1hour  360ltrs. x = ((x/8)  360)*12; x= 8640
_________________
Need Kudos to unlock GMAT Club tests



Intern
Joined: 23 Oct 2016
Posts: 34

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
12 Dec 2016, 08:50
let x be the rate of leakage, and V be the volume of the cistern
In first case (tap not turned on): x=v/8 liters/hour
=> 8*x=v
In second case (tap turned on): (x360)= V/12 liters/hour
=> 12*(x360)=v
Now, equating V:
12x  4320=8x 4x=4320 x=1080
=> v= 8*x=8*1080=8640 Liters
Hope this helps



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2248

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
22 Mar 2018, 15:42
anceer wrote: A cistern has a leak which empty it in 8 hrs, A tap is turned on which admits 6 liters a minute into the cistern, and it is now emptied in 12 hours, How many liters does the cistern hold ?
A. 8640 B. 8740 C. 8840 D. 8540 E. 8940 We can let x = the number of liters the cistern holds. Thus, the rate of the leak (outflow) is x/8 liters per hour. The rate of the tap (inflow) is 6(60) = 360 liters per hour. The net rate is the difference between the outflow and inflow, which is given as being equal to a net outflow of x/12 liters per hour. We can create the following equation: x/8  360 = x/12 Multiplying both sides by 24, we have: 3x  8640 = 2x x = 8640 Answer: A
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Intern
Joined: 18 Dec 2017
Posts: 6

Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which [#permalink]
Show Tags
23 Mar 2018, 08:49
The cistern is emptied in 8 hours > 8*x=y, with x=liters per minute and y=total capacity of liters
With the tap turned on, it takes 12 hours > 12* (x6)=y, note that "x6" because x is the speed at which the cistern is emptied, and if we pour 6 liters per minute more, we need to subtract them to x. So,
I. 8x=y II. 12 *(x6)=y
>x=18 Now, 8*18*60=y (times 60, because x was in liters per minute, not per hour, and 8 is the hourcount) >8*18*60= 18*480=8640=y
Hope it is helpful.




Re: A cistern has a leak which empty it in 8 hrs, A tap is turned on which
[#permalink]
23 Mar 2018, 08:49






