Two inlets P and Q are working on alternate hour for filling an empty

Question

Two inlets P and Q are working on alternate hour for filling an empty tank and only one inlet works at any point of time. How much time will it take to fill the tank completely?

1) Inlet P can fill the tank in 10 hours while working alone while Inlet Q takes 15 hours to fill the tank alone
2) Inlet P works for first hour to fill the tank

Source: https://www.GMATinsight.com

jainanurag470 · Answer

Hi

You posted two questions yesterday of same type as below:
Two inlets P and Q are working on alternate hour for filling an empty tank and only one inlet works at any point of time. How much time will it take to fill the tank completely?

1) Inlet P can fill the tank in 10 hours while working alone while Inlet Q takes 12 hours to fill the tank alone
2) Inlet P works for first hour to fill the tank

For this question according to you answer is C.

And for this question:

Two inlets P and Q are working on alternate hour for filling an empty tank and only one inlet works at any point of time. How much time will it take to fill the tank completely?

1) Inlet P can fill the tank in 10 hours while working alone while Inlet Q takes 15 hours to fill the tank alone
2) Inlet P works for first hour to fill the tank

You have given answer as A.

Kindly clarify the doubt or I am getting it wrong.

Thanks in advance.

rahitgs · Answer

Anurag, you have solved the sum in less than 7 seconds.. Put your pen to paper and see the difference for yourself.

Clue: In one of the 2 problem, the number of hours it will take to do the job will differ depending on who will go first.

jainanurag470 · Answer

Hi rahitgs

yes you are right I just missed it, actually i solved these two questions consecutively that's why i overlooked the data and options.

Anyways thank you.

varmashreekanth · Answer

Hi,

I also have the same question. Aren't both the questions same?
Also if we know the individual time taken by both the inlet pipes given, we still have to know which pipe works first right?

Can you help me understand, what am I missing ?

Thanks & Regards,
Shreekanth

jainanurag470 · Answer

Hi Shreekanth

These two questions may look same on first instance but the different values will lead to different answers.
Clue: The ques in which P takes 10 hrs and Q takes 15 hrs, the time to fill the tank will be same irrespective of which inlet pipe is used first. and another clue for both the questions just take the LCM of their hrs as the full capacity of the tank to reach the conclusion(I used this method) or the common multiple for eg in 10 hrs and 15 hrs case I took 300 ltrs as the capacity of tank .

Anurag Jain

I don't mind kudos

varmashreekanth · Answer

Thanks alot now I understood the difference.

fskilnik · Answer

job\,\, = { ext{fill}}\,\,{ ext{the}}\,\,{ ext{tank}} ?\,\,\,:\,\,\,{ ext{time}}\,\,\,{ ext{for}}\,\,{ ext{job}}\,\,\,\left( {{ ext{1 - h}}\,\,{ ext{alternating}}} ight) (1) Sufficient: Let´s imagine one job is defined by 30 identical tasks (30 = LCM(10,15)). From this statement, we know that: P does 3 tasks/h Q does 2 tasks/h In two hours 5 tasks are done, therefore in exactly 6*2 = 12 hours we have the job (6*5 = 30 tasks) done with P or Q starting ! Obs.: check this slightly different problem when you finish reading this one... https://gmatclub.com/forum/two-inlets-p ... 77483.html (2) Insufficient: If each inlet fills the tank in 2h, then ? equals 2h. If each inlet fills the tank in 3h, then ? equals 3h. The correct answer is therefore (A). This solution follows the notations and rationale taught in the GMATH method. Regards, Fabio.

stne · Answer

1) Inlet P can fill the tank in 10 hours while working alone while Inlet Q takes 15 hours to fill the tank alone.

In the first hour one would fill   \frac{1}{15}+ \frac{1}{10}= \frac{1}{6}

It doesn't matter which one operates first. In either case in the first two hours  \frac{1}{6}  work is done.

If   \frac{1}{6}  work is done is  2  hours then whole work is done in  12  hrs.

Caution: Do not forget to check the last fraction of work, some times the sequence of pumps do matter, but not in this case.

SUFF.

2) Inlet P works for first hour to fill the tank

We do not know the rate of other pump.

INSUFF.

Ans A

Hope it helps.

Two inlets P and Q are working on alternate hour for filling an empty

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Two inlets P and Q are working on alternate hour for filling an empty

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