Aptitude - Pipes and Cistern - Discussion

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?

i dont get this one.

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.

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

Thanks a lot. SRAVANREDDYPAILLA.

How did 1/20+1/24=11/120.
Please explain it ?

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

What is mean by galloons?

A measure of capacity for liquids. Say water or milk can be measured on gallons.

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.