Aptitude - Pipes and Cistern - Discussion

Let x be the minutes that B opened,
4(1/15 +1/20) + x (1/20) = 1.
x=10 2/3 => 10min 40sec.
After solving x = 10min 40sec +4 min =>14min 40 =>answer.

Let x be the minutes that B opened,
4 (1/15) + x (1/20) = 1.
After solving x = 14min 40sec => answer.

A = 15.
B = 20.
Lcm = 60.

Capacity A - 4
B - 3
(4+3)*4min = 28.
Remain 32.
By b only 32/3 = 10 2/3 ie 10m 40sec.
T time 14min 40sec.

@Vinay Kumar Gupta is absolutely Right.

The Answer is 10 Minutes And 40 Seconds.

Sol:
A=15minutes
B=20 minutes.

Taking LCM of Both Which comes 60.
Therefore Total capacity of the Tank is 60 litres,

For A: 15 * 4 = 60.
For B: 20 * 3 = 60.

It Means Pipe A Fills 4 Litres In 1 Minute.
And Pipe B Fills 3 Litres In 1 Minute,
Both ate filling 3+4=7 litres In 1 minute.
Both are Working For 4 minutes together.
Therefore, 7*4=28 litres.
Now total capacity - 28litres
60-28=32.

Now Pipe B Have To Fill These Remaining 32 litres,
As pipe B Fills 3 Litres in 1 minute.
So 3*10 = 30.
30 litres in 10 minutes.
As Pipe B Fills 3 litres in one minute means 1 litre in 20 seconds.
So, the remaining 2 litres Will take 40 seconds.
Therefore The Answer will be 10 minute's and 40 seconds.

@Sriganesh.

B can fill the tank in 1 min = 1/20 parts or work done of the tank.
After 4 min, B can alone to fill the remaining part of the tank?
min = 8/15 remaining parts or work done of the tank.
By cross multiply
1/20 parts = 1 min.
8/15 parts = ? min.
(8/15 * 1)/1/20 = ?
8/15 * 1 * 20 = ?
8/3*4 = ?
?=32/3=10 (2/3) min =10 min 40 sec (2/3 min convert to seconds 2/3 * 60=40 sec).

Thus, Total Time Required to fill the tank = 4 min + 10 min 40 sec.
= 14 min 40 sec.

Can anyone explain, why they multiplying 1 in (8/15) * (1*20)?

@Preeti.

Very clear solution. Thanks for explaining.

In the question, it asks about the time required. It is not asking about total time so the answer will be 10 minute and 40 seconds.

"1/20 :8/15 :: 1:x " I can't understand this. Please explain me.

a=15;
b=20;
l.c.m of 15,20=60;
a's 1Min=60/15 => 4;
b's 1Min=60/20 => 3;
(a+b)'s 4Min= (4+3)*4=28;
Now 60-28 = 32;
b remaining time = 32/3 => 10.66.
Now add 10.66+4 =>14.66.