Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

23 Dec 2015, 13:12

1

This post received KUDOS

4

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

89% (00:41) correct
11% (00:58) wrong based on 261 sessions

HideShow timer Statistics

At a constant Rate of flow, it takes 20 minutes to fill a swimming pool if a large hose is used and 30 minutes if a small hose is Used. At these constant rates, how many minutes will it take to fill the pool when both hoses are used simultaneously?

Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

24 Dec 2015, 03:42

1

This post received KUDOS

can be done in a few ways.

The std way

time taken to fill the pool by Large Hose =20 minutes =L or 1/L=1/20 similarly 1/S=1/30 simultaneously it will take 1/L+1/S=1/20+1/30=5/60=12 minutes

efficiency way (not necessarily the efficient way)

let l and s denote efficiency of large and small hose efficiency = 100/time take to fill the pool=100/30=3.33% for smaller hose similarly 100/20=5% for the larger hose working together 8.33% per minute time taken = 100/8.33 ===12.0048 ~ 12 minutes

This is a standard Work Formula question (2 or more 'entities' that work on a task together). When there are just 2 entities and there are no 'twists' to the question, we can use the Work Formula to get to the correct answer.

Work = (A)(B)/(A+B) where A and B are the individual times needed to complete the task.

We're told that two hoses take 20 minutes and 30 minutes, respectively, to fill a pool. We're asked how long it takes the two hoses, working together, to fill the pool.

(20)(30)/(20+30) = 600/50 = 12 minutes to fill the pool.

Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

12 Jan 2016, 19:51

EMPOWERgmatRichC wrote:

Hi All,

This is a standard Work Formula question (2 or more 'entities' that work on a task together). When there are just 2 entities and there are no 'twists' to the question, we can use the Work Formula to get to the correct answer.

Work = (A)(B)/(A+B) where A and B are the individual times needed to complete the task.

We're told that two hoses take 20 minutes and 30 minutes, respectively, to fill a pool. We're asked how long it takes the two hoses, working together, to fill the pool.

(20)(30)/(20+30) = 600/50 = 12 minutes to fill the pool.

The simple answer to your question is that we have to follow whatever 'instructions' we're given in the prompt. Here, we're given the two rates (time to fill the pool) in terms of 'minutes' and we're asked for an answer in 'minutes.' As such, there are no 'twists' or extra steps (and converting minutes to hours would like make all the work take longer).

If you're looking for more-complex Work questions, then you can search for them in the Quant Forums here.

Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

24 Jan 2017, 20:01

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.
_________________

Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

16 Mar 2017, 00:25

1

This post was BOOKMARKED

RSOHAL wrote:

At a constant Rate of flow, it takes 20 minutes to fill a swimming pool if a large hose is used and 30 minutes if a small hose is Used. At these constant rates, how many minutes will it take to fill the pool when both hoses are used simultaneously?

A. 10 B. 12 C. 15 D. 25 E. 50

In order to solve this question we need to know the combined work rate of the small hose and large hose.

Small Hose= 1 job / 20 mins

Large Hose= 1 job/ 30 mins

We must set the denominators equal and add the two fractions

3 jobs/ 60 mins + 2 jobs/ 60 mins = 5 jobs / 60 mins

Therefore

1 job / 12 mins- 1 job is done in 12 minutes at this combined work rate.

At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink]

Show Tags

06 May 2017, 17:48

1

This post received KUDOS

I had approached the question by picking numbers, but not sure if this is correct - can someone please verify if I what did below is correct or not?

Since in the question, they don't tell us the quantity to fill the pool with each hose, I just chose 60 liters as an estimate, therefore:

For large hose: 60L /20 min = 3L in 1 min For small hose: 60L/30 min = 2L in 1 min

Combined rates: 3L + 2L = 5L in 1 min together, so if we wanted to find how much it would take to fill up to the original 60L, that would mean you multiplied 5L by 12, therefore, 60 L would fill up in 12 min with the two hoses. Does this make sense or is the approach of picking numbers incorrect?

YES - your approach (TESTing VALUES) works just fine on this question. Since the prompt tells us nothing about the actual rates of the two hoses nor about the volume of the swimming pool, you can choose whatever values you like - as long as they properly account for the times that it takes the two hoses to fill the pool individually.