Aptitude - Pipes and Cistern - Discussion

@Senthil.

Lets start afresh,

If you think in terms of speed/rate of filling the tank of 'l' Litres capacity, then the speed of slower pipe will be x litre/min and the speed of faster pipe will be 3x litre/min.

But, if you think in terms of time, then the slower pipe will take x min(or 3x min) and the faster one will take x/3 min(or x min) to fill the tank.

Now, if you consider the second case i.e.,consider in terms of time, then you will only need to find out how much portion of the tank's capacity each pipe can fill in 36 min.

Since, in 1 min the slower pipe can fill 'l'/x litres of the tank's capacity(In x min 'l' litre), and

In 1 min the faster one can fill 'l'/(x/3) litres of the tank's capacity(In x/3 min 'l' litre).

Therefore, in 36 min slower pipe will fill 36*('l'/x) liters, And
In 36 min faster pipe will fill 36*('l'/(x/3)) liters.

Since, both the pipes are contributing in filling the tank of capacity 'l' Litres.

Therefore,

36*('l'/x) + 36*('l'/(x/3)) = 'l'.

('l'/x) + ('l'/(x/3)) = 'l'/36.

(1/x) + (1/(x/3)) = 1/36.

(1/x) + (3/x) = 1/36.

Hope, it will be clear now.

Why can't we take x+3x=36 and why we are taking 1/x+3/x=1/36 explain this solution in detail?

I have another solution,

Suppose slower pipe is taking X min, then in that time faster pipe will fill 3 tanks.

Now both start filling tanks,then when slower pipe will finishing filling till that time faster also done with filling 3 tanks.

Total number of tanks filled is Slower= 1, and faster = 3, sum total is 4 tanks, NOw time taken for filling 1 tank is 36, Therefore time taken for filling 4 tanks is 36*4 = 144.

Therefore it indicates same time taken by slower pipe also to complete fill the tanks.

I didn't understand the problem could you explain once.

Assume A = Fast pipe.

B = Slow pipe.

A takes x time. And B takes 3x time.

So, in 1 min 1/x + 1/3x = 1/36.

By solving 4x/3x^2 = 1/36.

Finally x = 4*36/3.

x = 48.

Time taken by slow pipe = 3x = 3*48 = 144 min.

I am getting a different answer,

Two pipe fills the tank in 36 min.

Let's take slower one = A.

Faster one as B.

So, B = A*3.

If B+A = 36.

Then B = 27 and A = 9.

If B alone has to fill the tank then it will fill in.

27min (of B) + 9/3 of A = 27+3 = 30 min.

And if go like this and A alone has to fill the tank then it would be:

30*3 = 90 min.

Why I this is not right someone Please explain?

Actually A=3B because A pipe fill d tank 3 times fast as B pipe.
So A=3B but in time.

Then B = A/3
Let, A= x-----(1) assume i.e B=x/3---------(2)

Formula 1/A+1/B=1/36 substitute both in
1/x+1/x/3 = 1/36,
1/x+3/x = 1/36,
4/x = 1/36.
=>x=4*36 =>144.

Great @Indrajit.

Most effective solution, Thanks @Laxman.

Thank you @Reshma.