# Aptitude - Pipes and Cistern - Discussion

### Discussion :: Pipes and Cistern - General Questions (Q.No.6)

6.

Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

 [A]. 60 gallons [B]. 100 gallons [C]. 120 gallons [D]. 180 gallons

Explanation:

 Work done by the waste pipe in 1 minute = 1 - 1 + 1 15 20 24

 = 1 - 11 15 120

 = - 1 .    [-ve sign means emptying] 40

 Volume of 1 part = 3 gallons. 40

Volume of whole = (3 x 40) gallons = 120 gallons.

 Shankarbalaji said: (Dec 26, 2010) 2 pipes can fill a tank in X and Y times respectively. How to calculate the time taken to fill the tank if both the pipes a open together?

 Zonked said: (Jan 4, 2011) i dont get this one.

 Karan Ratnaparkhi said: (Jan 7, 2011) As per the given condition we have 1/20 + 1/24 + 1/3 = 1/15. Here 1/3 refers to waste pipe nd 1/20, 1/24 refer to other 2 pipes.

 Sravanreddypailla said: (May 5, 2011) Two pipes can fill a tank in 20 and 24 minutes respectively and part filled by them is(1/20+1/24) 1gallon=~4litres All the three pipes working together total tank fills in 15min so 1part fills in 15min waste pipe can empty 3 gallons per minute so the volume of tank emptying by waste pipe is total filled tank minus part filled by to pipes i.e 1/15-(1/20+1/24) x 1min= -1/40 that means in 1min waste pipe is emptying 1/40part of total tank given , waste pipe can empty 3 gallons per minute therefore total volume is 1/40=3 gallons=>120 gallons hence capacity of tank is 120 gallons

 Manasa said: (Jun 11, 2011) Thanks a lot. SRAVANREDDYPAILLA.

 Raj said: (Apr 11, 2012) How did 1/20+1/24=11/120. Please explain it ?

 Rabi said: (Apr 18, 2012) Let the capacity of tank x gallons. then in 1 minute tank filled (x/20+x/24-3)gallons From the question we can write 15(x/20+x/24-3)=x [it took 15 min to fill x gallons] x/20+x/24-x/15=3 (6x+5x-8x)/120=3 3x/120=3 x=120 gallons

 Poonam said: (Feb 14, 2013) What is mean by galloons?

 Sowmi said: (Feb 20, 2013) A measure of capacity for liquids. Say water or milk can be measured on gallons.

 Krish said: (Apr 27, 2013) Let x = no.of minutes to take empty the gallon by leakage. (1/20+1/24-1/x)=1/15. x will get = 40 min. 40*3 = 120 gallon.

 Mouni said: (Jan 4, 2015) How did -1/40? Please explain it.

 Rupinder Kaur said: (Jan 5, 2015) How did 11/120?

 Arshiya said: (Mar 13, 2015) 11/120 is the time taken by two pipes to fill the tank.

 Bhakta B Monger said: (Jul 9, 2015) A = 20 minutes. B = 24 minutes. C = 3 gallons per minute. *The statement states that all three pipes working together can fill the tank in 15 minutes. Therefore we can express it as : A+B+C = 15 minutes. Say A+B+C=X. Then C = X- (A+B). Hence C = 15 minutes - (A+B). Making the values in the ratio one we get. C = 1/15- (1/20 + 1/24). = 1/15 - 11/120. = - 3/120. = -1/40. Thus the part filled by pipe C = 40 minutes. For the volume of tank: Given: Pipe C = 3 gallons per minute. Which means, in 1 minute = 3 gallons. Then in 40 minutes = x. x = 40*3 = 120 gallons.

 Dwarikesh Sharma said: (Jul 30, 2015) (1/20)+(1/24)-3G = (1/15). -3G = (1/15)-(1/20+1/24). -3G = -3/120. G = 1/120. Capacity of Tank G=120 gallon.

 Sujit Baji said: (Aug 19, 2015) (1/15 - 11/120) = -1/40 how? please explain it.

 Ragi said: (Nov 7, 2015) 15(x/20+x/24-3) = x. (11x-120)/8 = x. x = 40 gallon.

 Aniket said: (Dec 17, 2015) You can simply take the L.C.M of the values and get the result. L.C.M of above values = 2x2x2x3x5 = 120.

 Sreeram said: (Feb 8, 2016) A and B. Time: 20min and 24min. Efficiency: 6 and 5. Work done A+B in 1 min = 11. Work done A+B in 15 min = 11*15 = 165. Tank emptied by C in 15 min = 45. = 165 - 45 = 120 gallons.

 Snhk said: (Feb 17, 2016) L.C.M of 20, 15, 24 = 120 unit total capacity. 1st pipe = 6 unit. 2nd pipe = 5 unit. = 11 unit. Total 120/15 = 8 unit. 3rd (-) pipe capacity = (11 - 8) = 3 unit. As UTC 120. 3rd pipe can empty = 120/3 = 40 unit which is = 3 gallons per minute. Hence the capacity of the tank (40*3) =120 gallons.

 Nitin said: (Jun 15, 2016) L.C.M of 20, 15, 24 = 120 unit total capacity. 120/3 = 40. 40 * 3 = 120.

 Sindhu said: (Jun 28, 2016) Why making the values in the ratio one we get. C = 1/15 - (1/20 + 1/24).

 S.N.Raju said: (Jul 20, 2016) Given, First pipe takes 20h. Second pipe take 24h. ALL together take 15h. Assuming that capacity of tank L. C. M [20, 24, 15] = 120. First pipe can fill 6u/m. Second pipe fill 5u/m. All three fill 8u/m -------> 1. First and second together fill in 11m/u----------> 2. From 1 and 2 we get; Third pipe fills the tank in 3u/m that is 120/3 = 40u of total fill. But given 3 gallons are empty. 3 * 40 = 120gallons (capacity of tank).

 Ashutosh Sahani said: (Jul 21, 2016) 120 gallon is waste water, which drains out from the tank in 15 min.

 Nasir said: (Aug 16, 2016) Let, the capacity of the tank is x gallon. 3 pipes 1 min can fill up (1 / 20 +1 / 24 - 3), So, 15 min can fill up, 15 (1 / 20 + 1 / 24 - 3), We get 15 (1 / 20 + 1 / 24 - 3) equally to x. We get the calculation of x is 120 gallons.

 Aqueeb Khan said: (Sep 4, 2016) How can we solve this problem by the unitary method?

 Md.Gohor Rizvi. said: (Oct 17, 2016) Let the capacity of the tank or pump X gallons. The first pipe can fill the tank in 20 min. The second pipe can fill the tank in 24 min. 1st pipe 20 min. fill X gallon. So, First pipe in one min can fill X/20 gallons. So, the second pipe can fill in X/24 gallons. And the third pipe flows out 3 gallons per minute. So, X/20 + X/24 - 3 equal X/15 therefore X equal 120 gallons.

 Siddhesh said: (Apr 20, 2017) The part of tank filled in 1 min by all pipes=(1/20)+(1/24)-(1/x). = (44x-480)/480x. The time required to fill 1 tank. = 480x/(44x-480) minutes. Where, x = time in minutes required to empty the tank by the waste pipe. But all pipes fill the total tank in 15 minutes. So, 15 = 480x/(44x-480). x = 40 minutes. The capacity of tank = discharge per minute * time. = 3 * 40, = 120 gallons.

 Pritesh Bhawsar said: (Jul 27, 2017) I have the best solution here. take LCM of 20,24 = 120 Pipe c can empty 3 gallon/minute. 120/3 = 40 minute. -----------------------------| minute | efficiency | -------------|---------------| a = 20 | 6 | b = 24 | 5 | c = 40 | 3 | ****************************** (a+b-c) --> 11-3 = (+8) 120/8 = 15 minute. 120-gallon tank will fill in 15 minutes, A can fill in 24 minutes or 5 gallons/minute, B can fill in 20 minutes or 6 gallons/minute. C can empty in 40 minutes or 3 gallons/minute <---question says.

 Tubai said: (Jul 27, 2017) Your logic is most acceptable or easy to me, Thanks @Rabi.

 Prasna said: (Jan 3, 2018) Take the LCM of 24 and 20, you will get the Answer is 120.

 Puja Banerjee said: (Jan 25, 2018) Thanks for the explanation @Bhakta B Monger.

 Swapnil said: (Feb 7, 2018) Let , the time taken by waste pipe to empty the tank is x. Then part feed in one min. (1/20+1/24) - 1/X = 1/15 11/120 -1/X = 1/15, 11X-120/120X = 1/15, 165X -1800= 120 X, By solving we get x = 40 min. So 40 min is the time which is taken by waste pipe to empty the entire tank In problem it is given that waste pipe discharge 3 gallons per min. 40*3= 120 gallons is a capacity of tank.

 Somi said: (May 22, 2018) Thank you @Swapnil.

 Somi said: (May 22, 2018) Thank you @Swapnil.

 Rakhshanda said: (Jul 29, 2018) How 3 gallons =1/40?

 Vishal Gawali said: (Aug 7, 2018) We can directly determine the total capacity of tank by taking LCM of 20 24 15 as 120.

 Shyam said: (Feb 3, 2019) How this relation come 1/A+1/B+1/C = 1/15? Third pipe can empty tank that means 1/A+1/B-1/C = 1/15.

 Bagga said: (Jun 8, 2019) A=20m, B=24m, Let c=x min. Now LCM= 120x(Let Capacity of Tank). Part filled per min: A = 6x. B = 5x. C = 120. Now given tank filled in 15 min. therefore, 120x/11x-120 = 15. solve this x = 40. Now given C fills 3 Gallon in 1 min which is its efficiency. Hence 40 * 3 = 120 Capacity of Tank.