Working alone, pump A can empty a pool in 3 hours. Working alone, pump

Speed of B is 1.5 times of A .
combined speed B+A = 1.5A + A = \(\frac{5}{2}\) A . so if ideally A takes 3 hrs , with \(\frac{5}{2}\) *A speed it will take --> \(\frac{3*2}{5}* 60\) = 72 minutes.

Answer A.

Answer = A = 72

Rate of pump A \(= \frac{1}{180}\)

Rate of pump B = \(\frac{1}{120}\)

Combined rate \(= \frac{5}{360}\)

Time required for combined work \(= \frac{360}{5} = 72\)

Let the total work be 1
Rate of work A = Total work done/ Total time taken = 1/3
Rate of work B = Total work done/ Total time taken = 1/2

Total Rate \(= 1/2 + 1/3 = 5/6\)
In 1 hour work done is = 5/6
Time taken to complete the entire work (1) = 6/5 hours

\((6/5)*60 = 72\) minutes.

Answer A

Hi All,

In this prompt, we have two 'entities' sharing a task (with no *twists*), so the Work Formula will be perfect for this question.

Work = (A)(B)/(A+B) where A and B are the rates of the two entities.

We're given the respective rates for two pumps to empty a pool:

Pump A can empty the pool in 3 hours.
Pump B can empty the pool in 2 hours.

We're asked how long it takes the two pumps, working together, to empty the pool.

Plugging in the respective numbers (the 3 and the 2), we have...

(3)(2)/(3+2) = 6/5 = 1.2 hours = 1 hour 12 minutes

The question asks for an answer in MINUTES. 1 hour 12 minutes = 72 minutes.

Final Answer:

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

Combined rate is 1/3+1/2 is 5/6.

time taken to empty pool is 6/5*60 = 72 Mins
Answer is A

Total Work Done in 1 hr = (1/2) +(1/3)

Total time in minutes = 6/5 *60 = 72 minutes

Ans : A

+1 for A
IN 1 hour, Pump A can empty=1/3 of the pool
In 1 hour, Pump B can empty=1/2 of the pool
Working together, in 1 hour, they can empty=1/3+1/2=5/6 of the pool
Therefore, to empty the pool. both will take=6/5 Hours=6/5*60 minutes=72

MAGOOSH OFFICIAL SOLUTION:

The combined rate of pumps A and B is:

1/3 + 1/2 = 2/6 + 3/6 = 5/6, so the time is 1/(5/6) = 6/5 hours, which is 6/5 x 60 = 72 minutes.

Answer: A

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.