# Aptitude - Pipes and Cistern - Discussion

### Discussion :: Pipes and Cistern - General Questions (Q.No.2)

2.

Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:

[A].
 1 13 hours 17
[B].
 2 8 hours 11
[C].
 3 9 hours 17
[D].
 4 1 hours 2

Explanation:

 Net part filled in 1 hour 1 + 1 - 1 = 17 . 5 6 12 60 The tank will be full in 60 hours i.e., 3 9 hours. 17 17

 Ang said: (Sep 26, 2010) Why we didnt take ( 1/12 - (1/5+1/6) ). Here 12 is greater right?

 Karan Ratnaparkhi said: (Jan 7, 2011) 1/12 is smaller dan other two

 Komal said: (Feb 10, 2011) Why we take 17/60 as 60/17 in the next step ?

 Jyothi said: (Feb 24, 2011) @komal net part in 1 hour is 17/60 part so in 60/17 hour the part will be 1 here 1 means tank is full..... its just like the time and wok concept...

 Obama Sells Credits For Banks said: (Apr 15, 2011) Why we take 17/60 as 60/17 in the next step ?

 Sathya said: (Jun 2, 2011) Can't understood. Explain clearly.

 Manasa said: (Jun 11, 2011) Here pipes A and B are used for filling the tanks, A and B takes 5 and 6 hours respectively to fill the tank . for 1 hour ,A can fill 1/5th of the tank and B can fill 1/6th of the tank. now tank C is used foe emptying the tank(water is running off from the tank)..it can empty the tank in 12 hours..means for 1 hour it empties 1/12th of water from the tank NOTE: A and B are filling the tank whereas C is used for emptying the tank. therefore add A and B and subtract it from c now consider how much water gets filled in the tank in 1 hour, 1/5+1/6-1/12=17/60 for 1 hour----17/60 ? hours----1 (note: for 1 hour-- 17 parts got filled up out of 60 parts for "?"hours-- 60 parts get filled up out of 60 (60/60=1) Here 1 indicates tank gets filled) just by cross multiplying it (1*1)=(?*17/60) ?=(17/60)/(1*1) 60/17 hours it can fill the tank.

 Preeti said: (Sep 13, 2011) Thanks Manasa. I got it clearly.

 Neha said: (Jan 20, 2012) (1/5 + 1/6 - 1/12) = (6+5/30 - 1/12) = (11/30 -1/12) = (132-30/360) = (102/360)dividing numerator &denominator by 2 = (51/180)dividing numerator &denominator by 2 = (17/60)

 Deepi said: (Feb 5, 2012) Hi guys use this concepts to find the solution in easily Concept 1: A fill tank in x hrs and B fill in Y hrs and C in z hrs means together fill=? A&B=X*y/x+y let that A&B ans as p then A,B&C=p*z/p+z Concept 2: A fill tank in x hrs and B empty in Y hrs then both together work how much time is to empty=? =x*y/y-x

 Rav said: (Feb 16, 2012) Will it work in every case ?

 Divya said: (Feb 26, 2012) Thanks manasa.

 Mageswari said: (Jul 29, 2012) Thanks manasa your explanation is clear cut.

 Rohit said: (Aug 27, 2012) Thanks neha.

 Kiran said: (Oct 12, 2012) @kaveri 1/5+1/6+-1/12= L.C.M of 5,6,12=60 So 1/5+1/6-1/12 12+10-5 --------------= 17 60 -------- 60

 Alka said: (Oct 17, 2012) @Happy. First of all take L.C.M of 5, 6, &12. Then divide this L.C.M with every numerator & multiply that value with denominator of same.

 Subrat Kumar Dhani said: (Feb 13, 2014) A PIPE - 5HRS. B PIPE- 6HRS. C PIPE - 12HRS TO EMPTY IN TANK, SO THAT, A-5 B-6 C-12 (TOTAL L.C.M 60 UNIT TANK CAPACITY). A-12UNIT, B-10UNIT ,C-5UNIT. TOGETHER(A+B)-EMPTY(C) = 12+10-5 = 17. TOTAL UNIT 60/17 = 3.52

 Sameera said: (Aug 10, 2014) Thanks manasa but I can't understand one point ie;c is used for emptying of tank & when a&b are used to filling of water so when we use the 3 pipes simultaneously then at any time or at any point the will not be FILL so how can we conclude with a simple answer.

 Nelson said: (Dec 3, 2014) @Sameera, the tank will be filled as you can see the rate of filling is more than the rate of emptying. If the tank can't be filled, then the math would have told us so.

 Aryan Kanti said: (Apr 27, 2015) How do we find the time taken?

 Anita Sahoo said: (Oct 19, 2015) 1/5+1/6-1/12=17/60. How it possible? 1/5+1/6-1/12=-1/20. Why not? Please explain.

 Anita Sahoo said: (Oct 19, 2015) @Subrat please tell me how C is 5?

 Bijayalaxmi said: (Dec 3, 2015) Formula: xyz/yz+xz-xy.

 Pranav Kumar said: (Dec 3, 2015) I didn't understand this problem and can some one make it clear.

 Ajmal said: (Dec 3, 2015) How 60/17 can write as 3*9/17?

 Sushmitha said: (Dec 21, 2015) 17)60(3 51 = 60-51 = 9. Then q*(r/d). i.e 3*9/17.

 Sandeep said: (Jan 28, 2016) Can you please explain it clearly that how we get 3*9/17?

 Rakesh said: (Mar 24, 2016) @Alka your answer is best, so thanks.

 Rahul Namdev said: (Apr 28, 2016) @Kaveri. Pipe A =1/5 hrs & B=1/6 hrs, & C=/12 hrs. LCM of 5, 6 , 12 = 60. Units or liter (whatever) of : A = 5 (hours)/60(units) = 12 units. B = 6 (hours)/60(units) = 10 units. C = 12 (hours)/60(units) = 5 units. Now, add A + B(inlet pipe) - C (outlet pipe)/ 60. --> 22 - 5/60. ---> 17/60.

 Shruthi G.R said: (Jul 12, 2016) Can you please once again clear how it comes 60/17 in hours 3 * 9/17?

 Neha said: (Aug 17, 2016) In 17/60 60 is LCM of numbers but how 70 comes?

 Jerry said: (Jan 11, 2017) Thank you @Manasa.

 Ramya said: (Jan 29, 2017) Thank you @Manasa.

 Rohit said: (Apr 7, 2017) Thanks @Manasa.

 Anish Gupta said: (Apr 13, 2017) @Neha Just forget that LCM part if 17tank is filled in 60hours the how many tank will be filled in 1 hour. 17tank = 60hours 1tank = x, 17 * x = 60 * 1tank = x = 60/17.

 Mahesh said: (May 6, 2017) How the 17 came? Please explain me.

 Prabhat said: (Jun 13, 2017) Just take it by formula. 5 * 6 * 12/6 * 12+ 5 * 12-5 * 6 = 60/17.

 Brijesh said: (Mar 6, 2018) How option C is right? How comes 60/17?

 Naushad said: (Mar 11, 2018) Dear Sir, I think the pipes that filling the tank operates under constant pressure. So the flow rate is constant. But the pipe that is draining is operating under varying head, ie. Under varying pressure. So the draining of tank is not uniform, but proportional to the square root of the head. Hence the problem can't be solved using simple mathematics. For centuries we put it in wrong way.

 Showkat Bhat said: (Sep 6, 2018) (1/5 + 1/6 - 1/12) = (6+5/30 - 1/12). = (11/30 -1/12), = (132-30/360), = (102/360)dividing numerator &denominator by 2, = (51/180)dividing numerator &denominator by 3, = (17/60).

 Amudha said: (Oct 26, 2018) How it will come 17/60 to 60/17?

 Kavi said: (Nov 1, 2018) @Neha how? (51/180)dividing numerator &denominator by 2. = (17/60).

 Subiksha said: (Dec 20, 2018) I can't understand this. Anyone explain me clearly?

 Shekhar said: (Mar 18, 2019) How 60/17 is converted into 3 (9/17)? Please explain.

 Ragavi said: (Jun 6, 2019) How to calculate it when the time is in minutes (intsead of hrs)? Please tell me.

 Lavanya said: (Jul 30, 2019) Thanks all.

 Rupa said: (Nov 27, 2019) @Sekhar. 17*3+9/60 = 60/17.

 Sireeshadevi Koppisetti said: (Apr 5, 2020) Thanks @Subrat Kumar Dhani.

 Marion said: (Feb 9, 2021) How does 60/17 become 39/17? Explain me.

 Biswanath Tripathy said: (Feb 19, 2021) How it is possible? Explain, please.

 Naren said: (Feb 23, 2021) Thanks for explaining @Manasa.