Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 12)
12.
A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half?
Answer: Option
Explanation:
| Part filled by (A + B) in 1 minute = |  |
1 | + | 1 |  |
= | 1 | . |
| 60 | 40 | 24 |
Suppose the tank is filled in x minutes.
| Then, | x | |
1 | + | 1 | |
= 1 |
| 2 | 24 | 40 |
 |
x | x | 1 | = 1 |
| 2 | 15 |
x = 30 min.
Discussion:
51 comments Page 4 of 6.
Sameer kapoore said:
1 decade ago
Mine answer is coming 32 mins. By LCM method I am getting different answer.
A = 60 min.
B = 40 min.
By taking LCM total work is 120 unit. (say litre).
So a fills the tank in 120/60 = 2 litre/min.
B does it in 120/40 = 3 litre/min.
Together 5 litres. So time taken by both a and b to complete work is 120/5 = 24 min.
Now half tank means capacity of 60 litres. (60+60=120).
Now half the tank is filled by a+b=60/ (3+2) =12 min.
And half the tank is filled by b only = 60/3=20 min.
So therefore, 12+20=32 min.
A = 60 min.
B = 40 min.
By taking LCM total work is 120 unit. (say litre).
So a fills the tank in 120/60 = 2 litre/min.
B does it in 120/40 = 3 litre/min.
Together 5 litres. So time taken by both a and b to complete work is 120/5 = 24 min.
Now half tank means capacity of 60 litres. (60+60=120).
Now half the tank is filled by a+b=60/ (3+2) =12 min.
And half the tank is filled by b only = 60/3=20 min.
So therefore, 12+20=32 min.
Sree said:
1 decade ago
@suresh.
What you explained was very simple & easy to understand. But in the question its mentioned leaking the Time taken by pipe (B) & time taken by both pipes (A+B). So how can we subtract 50-20?
What you explained was very simple & easy to understand. But in the question its mentioned leaking the Time taken by pipe (B) & time taken by both pipes (A+B). So how can we subtract 50-20?
Abhishek said:
1 decade ago
@Salini.
I completely agree to your let method and the what question is saying. But through LCM method also answer would be 28 min 48 seconds.
I completely agree to your let method and the what question is saying. But through LCM method also answer would be 28 min 48 seconds.
Suresh said:
1 decade ago
Here in this question they give a = 60, b = 40.
Then half of the b is = 20.
After half of the a and b that means a+b/2 = 60+40/2 = 50.
Then, 50-20 = 30.
Then half of the b is = 20.
After half of the a and b that means a+b/2 = 60+40/2 = 50.
Then, 50-20 = 30.
Salini said:
1 decade ago
@Madhu.
Here you are considering that B does half of work but in question they had mention only the half of time B does the work. Please clarify my doubt.
Here you are considering that B does half of work but in question they had mention only the half of time B does the work. Please clarify my doubt.
Salini said:
1 decade ago
By LCM method I am getting different answer.
A = 60 min.
B = 40 min.
By taking LCM total work is 120 unit.
So A does 120/60 = 2 unit.
B does 120/40 = 3 unit.
Together 5 unit so time taken by both A and B to complete work is 120/5 = 24 min.
It means B will work alone for 12 min and work done by B is 12x3 = 36 unit.
Remaining work is 120-36 = 84 unit which is done by both A and B so 84/5 = 16.8 min.
Then total time taken is = 12+16.8 = 28.8 min.
A = 60 min.
B = 40 min.
By taking LCM total work is 120 unit.
So A does 120/60 = 2 unit.
B does 120/40 = 3 unit.
Together 5 unit so time taken by both A and B to complete work is 120/5 = 24 min.
It means B will work alone for 12 min and work done by B is 12x3 = 36 unit.
Remaining work is 120-36 = 84 unit which is done by both A and B so 84/5 = 16.8 min.
Then total time taken is = 12+16.8 = 28.8 min.
Madhu reddy said:
1 decade ago
So simple.
a =60; b= 40; a+b = 60*40/60+40 = 24 (formula).
Let's take tank capacity 2x min (i.e x+x).
x/40 + x/24 = 1 (full tank).
By solving, we get x = 15 min.
Therefore 2x = 2*15 = 30 min.
a =60; b= 40; a+b = 60*40/60+40 = 24 (formula).
Let's take tank capacity 2x min (i.e x+x).
x/40 + x/24 = 1 (full tank).
By solving, we get x = 15 min.
Therefore 2x = 2*15 = 30 min.
Joy Prakesh said:
1 decade ago
Anyone can give any explanation of @Sri's comment?
Sri said:
1 decade ago
Please check the answer is 32 minutes,
B can fill a tank in 40 minutes means it can fill half tank by 20 minutes
Half tank B = 20 minutes.
A and B can fill a tank in 24 minutes means it can fill half tank by 12 minutes
Half tank A+B = 12 minutes
So, the answer is 32 minutes.
B can fill a tank in 40 minutes means it can fill half tank by 20 minutes
Half tank B = 20 minutes.
A and B can fill a tank in 24 minutes means it can fill half tank by 12 minutes
Half tank A+B = 12 minutes
So, the answer is 32 minutes.
Tom said:
1 decade ago
I don't understand that how 1/40 is for one minutes?
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