At a constant Rate of flow, it takes 20 minutes to fill a swimming poo : GMAT Problem Solving (PS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 24 Jan 2017, 11:53

### GMAT Club Daily Prep

#### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

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

Author Message
TAGS:

### Hide Tags

Joined: 27 Sep 2015
Posts: 63
GMAT 1: 410 Q33 V13
WE: Management Consulting (Computer Software)
Followers: 4

Kudos [?]: 40 [0], given: 26

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

### Show Tags

23 Dec 2015, 12:12
00:00

Difficulty:

5% (low)

Question Stats:

93% (01:40) correct 7% (01:12) wrong based on 82 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?

A. 10
B. 12
C. 15
D. 25
E. 50
[Reveal] Spoiler: OA

_________________

Discipline does not mean control. Discipline means having the sense to do exactly what is needed.

Senior Manager
Joined: 20 Feb 2015
Posts: 389
Concentration: Strategy, General Management
Followers: 2

Kudos [?]: 63 [0], given: 10

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

### Show Tags

24 Dec 2015, 02:42
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
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 8344
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 382

Kudos [?]: 2474 [0], given: 164

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

### Show Tags

26 Dec 2015, 09:10
Expert's post
1
This post was
BOOKMARKED
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.

[Reveal] Spoiler:
B

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

# Rich Cohen

Co-Founder & GMAT Assassin

# Special Offer: Save $75 + GMAT Club Tests 60-point improvement guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Manager Joined: 28 Dec 2013 Posts: 80 Followers: 0 Kudos [?]: 1 [0], given: 3 Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink] ### Show Tags 12 Jan 2016, 18:51 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. Final Answer: [Reveal] Spoiler: B GMAT assassins aren't born, they're made, Rich But how do we know when we have to convert minutes to hours? What is an example of a more twisted problem? EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 8344 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 382 Kudos [?]: 2474 [1] , given: 164 Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo [#permalink] ### Show Tags 12 Jan 2016, 19:19 1 This post received KUDOS Expert's post HI sagnik242, 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. GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

60-point improvement guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Re: At a constant Rate of flow, it takes 20 minutes to fill a swimming poo   [#permalink] 12 Jan 2016, 19:19
Similar topics Replies Last post
Similar
Topics:
10 An empty bucket being filled with paint at a constant rate takes 6 min 9 30 Jun 2015, 03:56
20 Jim takes a seconds to swim c meters at a constant rate from 14 08 Jan 2013, 03:14
20 An empty pool being filled with water at a constant rate 15 20 Dec 2012, 04:53
14 Jim takes a seconds to swim c meters at a constant rate 16 07 Dec 2012, 19:12
22 The water from one outlet, flowing at a constant rate, can 10 23 Mar 2012, 20:18
Display posts from previous: Sort by