Working together at their respective rates, two hoses fill a pool in 2

Question

Working together at their respective rates, two hoses fill a pool in 2 hours. If one of the hoses, working alone, could fill the pool in 3 hours, how long would it take the other hose to fill the pool alone?

A. 2 hours
B. 3 hours
C. 4 hours
D. 5 hours
E. 6 hours

A. 2 hours
B. 3 hours
C. 4 hours
D. 5 hours
E. 6 hours

sashiim20 · Answer

Let the hoses be  A  and  B .

Given  A  and  B  hoses together can fill a pool in  2  hours.

Therefore  1  hour work of  A  and  B  together is equal to.

\frac{1}{A} + \frac{1}{B} = \frac{1}{2}

Given  A  could fill the pool in  3  hours alone.

Therefore,  A = 3  hours

\frac{1}{3} + \frac{1}{B} = \frac{1}{2}

\frac{1}{B} = \frac{1}{2} - \frac{1}{3} = \frac{3-2}{6} = \frac{1}{6}

B = 6  hours

Therefore  B  can fill the pool alone in  6  hours.

Answer (E)...

Luckisnoexcuse · Answer

Pool is 6 units
Hose A + Hose B = 3 units/hr
Hose A = 2 units/hr

Hose B = 1 unit/hr
Time = 6/1 = 6 hrs
E

EMPOWERgmatRichC · Answer

Hi All,

This question is a standard example of a Work Formula question (with 2 'entities' working on a job together). When this type of question has no 'quirks' to it (such as 3 or more entities or one of the entities stops working partway through the job), you can use the Work Formula to answer it:

Work = (A)(B)/(A+B) = amount of time to complete the job while working together (where A and B are the two individual times it takes to do the job).

In this prompt, we know that one of the hoses takes 3 hours to do the job alone and that the two hoses (working together) can complete the job in 2 hours....

(3)(B)/(3+B) = 2 hours 
3B = (2)(3+B) 
3B = 6 + 2B 
B = 6 hours

Thus, it would take the second hose 6 hours to fill the pool by itself.

Final Answer:  E

GMAT assassins aren't born, they're made, 
Rich

ScottTargetTestPrep · Answer

We can let n = the time, in hours, it takes the other hose to fill the pool alone. Thus, the rate of that hose = 1/n. Since the rate of the known hose = 1/3 and the combined rate = 1/2, we have:

1/n + 1/3 = 1/2

Multiplying by 6n, we have:

6 + 2n = 3n

6 = n

Thus, the other hose takes 6 hours to fill the pool.

Answer: E

pushpitkc · Answer

Since one of the hoses fills the pool in 3 hours and both the hoses 
fill the pool in 2 hour, we should assume a number divisible by both 
these numbers to be the total capacity of the pool. Let that be 60 units.

Let the hose which can fill the pool alone in 3 hours be hose A, so the
rate of work is 20 units/hour. Similarly, both the hoses can fill the pool
in 2 hours, and must fill 30 units/hour.

Hence, the other hose must be filling the pool at the rate of 10 units/hr

Therefore, the time taken to fill the entire pool is  \frac{60}{10}  (6 hours - Option E)

BrentGMATPrepNow · Answer

Another approach is to  assign a nice value to the job . 
In this case, we need a value that works well with the given information (2 hours and 3 hours). 
So, let's say the job consists of filling a pool containing  6  liters of water

One of the hoses, working alone, takes 3 hours to fill the pool   
We'll call this hose A. 
Let A = the rate of work of this hose 
If it takes 3 hours for this hose to fill a  6 -liter pool, then.... 
A =  6 /3 = 2 liters per hour (since rate = output/time)

Working together at their respective rates, two hoses fill a pool in 2 hours.   
Let B = the rate of work of the other hose 
So, the COMBINED rate = A+B 
If it takes 2 hours for the combined hoses to fill a  6 -liter pool then.... 
A+B =  6 /2 = 3 liters per hour (since rate = output/time)

So, if A = 2 liters per hour, and A+B = 3 liters per hour 
Then we can see that  B = 1  liter per hour

How long would it take the other hose (hose B) to fill the pool alone?   
Time = output/rate =  6 / 1  = 6 hours

Answer: E

Cheers, 
Brent

Abhishek009 · Answer

Let the total capacity of the pool be 6 units

Efficiency of A + B = 3 units/hr
Efficiency of B = 2 units/hr

So, Efficiency of A = 1 unit/hr

Thus, time required to fill the pool alone is 6 hours, answer will be (E)

bumpbot · Answer

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Working together at their respective rates, two hoses fill a pool in 2

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