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

Question

Working alone, pump A can empty a pool in 3 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?

A. 72
B. 75
C. 84
D. 96
E. 108

Kudos for a correct  solution .

ngie · Accepted Answer

Rate of A:  \frac{1}{3h} 
Rate of B:  \frac{1}{2h} 
Combined rate:  \frac{1}{3h}+\frac{1}{2h}=\frac{5}{6h}=\frac{5}{360 minutes}=\frac{1}{72 minutes}

Answer A is correct

nachobioteck · Answer

Pump A can empty the pool in 3 hours therefore the rate at which it empties is 1/3 pool/hour
Pump b can empty the pool in 2 hours therefore the rate at which it empties is 1/2 pool/hour.

If they work together, the resulting rate is the addition of both rates (1/3 +1/2)pool/hour = 5/6 pool/hour

Now we have the following:

(5/6pool)/60min = 1pool/x

x = 72minutes

Answer is A

Lucky2783 · Answer

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.

PareshGmat · Answer

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

earnit · Answer

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

EMPOWERgmatRichC · Answer

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:  A

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

Celerma · Answer

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

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

dream21 · Answer

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

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

Ans : A

KS15 · Answer

+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

Bunuel · Answer

MAGOOSH OFFICIAL SOLUTION: pumpsaandb_text.PNG

ScottTargetTestPrep · Answer

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

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

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

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards