Find all School-related info fast with the new School-Specific MBA Forum

It is currently 27 Jul 2016, 18:39
GMAT Club Tests

Close

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
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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

A small water pump would take 2 hours to fill an empty tank

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
Joined: 05 Dec 2011
Posts: 10
WE: Information Technology (Computer Software)
Followers: 0

Kudos [?]: 23 [0], given: 11

A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 07 Feb 2012, 07:00
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

82% (01:50) correct 18% (00:54) wrong based on 292 sessions

HideShow timer Statistics

Can someone assist me with solving this question?

A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time?

A) 1/4
B) 1/3
C) 2/5
D) 5/4
E) 3/2
[Reveal] Spoiler: OA
Expert Post
4 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 34092
Followers: 6094

Kudos [?]: 76664 [4] , given: 9978

Re: Quant PS [#permalink]

Show Tags

New post 07 Feb 2012, 07:09
4
This post received
KUDOS
Expert's post
3
This post was
BOOKMARKED
domu904 wrote:
Can someone assist me with solving this question?

A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time?

A) 1/4
B) 1/3
C) 2/5
D) 5/4
E) 3/2


Rate of the small pump is 1/2 tank/hour (rate is reciprocal of time);
Rate of the larger pump is 2 tank/hour;

Combined rate of the two pumps is 1/2+2=5/2 tank/hour, hence together they will fill the empty tank in 1/(5/2)=2/5 hours (time=job/rate).

Answer: C.

Theory on work/rate problems:
two-consultants-can-type-up-a-report-126155.html?hilit=know%20rate%20work%20reciprocal#p1030079
work-word-problems-made-easy-87357.html

Hope it helps.

P.S. Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/ and DS questions in the DS subforum: gmat-data-sufficiency-ds-141/

No posting of PS/DS questions is allowed in the main Math forum.
_________________

New to the Math Forum?
Please read this: All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 10619
Followers: 495

Kudos [?]: 130 [0], given: 0

Premium Member
Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 07 Jan 2014, 04:59
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 10619
Followers: 495

Kudos [?]: 130 [0], given: 0

Premium Member
Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 10 Jan 2015, 07:21
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Expert Post
1 KUDOS received
EMPOWERgmat Instructor
User avatar
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 6909
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 300

Kudos [?]: 2045 [1] , given: 161

Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 10 Jan 2015, 13:31
1
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
Hi All,

We're given the rates of two entities that will share a job together - this is the standard "set-up" for a Work Formula question.

Work Formula = (A)(B)/(A+B) where A and B are the respective amounts of time needed to individually complete a job.

Pump A = 2 hours to fill a tank
Pump B = 1/2 hour to fill a tank

Working together, it takes....

(2)(1/2)/(2 + 1/2) = 1/2.5 hours to fill the tank together...

1/2.5 = 2/5 hours

Final Answer:
[Reveal] Spoiler:
C


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!***********************

Intern
Intern
avatar
Joined: 29 Nov 2015
Posts: 13
Followers: 0

Kudos [?]: 5 [0], given: 44

Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 29 Dec 2015, 11:08
Bunuel wrote:
domu904 wrote:
Can someone assist me with solving this question?

A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time?

A) 1/4
B) 1/3
C) 2/5
D) 5/4
E) 3/2


Rate of the small pump is 1/2 tank/hour (rate is reciprocal of time);
Rate of the larger pump is 2 tank/hour;

Combined rate of the two pumps is 1/2+2=5/2 tank/hour, hence together they will fill the empty tank in 1/(5/2)=2/5 hours (time=job/rate).

Answer: C.



Hi, the logic I used was pretty much the same as yours, still Idk where I went wrong...

small pump fills 1 tank in 2 hours -> 1/2 tank in 1 hour -> 1/4 tank in 1/2 hour
big pump fills 1 tank in 1/2 hour

1/4 + 1 = 5/4 work which will take 4/5 hours
Expert Post
1 KUDOS received
EMPOWERgmat Instructor
User avatar
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 6909
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 300

Kudos [?]: 2045 [1] , given: 161

Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 29 Dec 2015, 23:46
1
This post received
KUDOS
Expert's post
Hi sarathvr,

With the work that you've done, you have calculated how much of the tank would be filled in 1/2 an hour by the two pumps (working together).

In 1/2 hour:
The small pump would fill 1/4 of the tank
The large pump would fill 1/1 of the tank

Combined, that is 1/4 + 4/4 = 5/4 of the tank in 1/2 an hour. This means that the two pumps would OVER-FILL the tank in 1/2 an hour. By extension, it would take LESS than 1/2 an hour to fill the tank, so the answer CAN'T be 4/5 of an hour.

If you're going to use this approach, then you would have to MULTIPLY both sides by 4/5....

(5/4 of a tank)(4/5) = (1/2 hour)(4/5)
20/20 of a tank = 4/10 of an hour
1 tank = 2/5 of an hour

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!***********************

Intern
Intern
avatar
Joined: 29 Nov 2015
Posts: 13
Followers: 0

Kudos [?]: 5 [0], given: 44

Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 30 Dec 2015, 07:33
EMPOWERgmatRichC wrote:
Hi sarathvr,

With the work that you've done, you have calculated how much of the tank would be filled in 1/2 an hour by the two pumps (working together).

In 1/2 hour:
The small pump would fill 1/4 of the tank
The large pump would fill 1/1 of the tank

Combined, that is 1/4 + 4/4 = 5/4 of the tank in 1/2 an hour. This means that the two pumps would OVER-FILL the tank in 1/2 an hour. By extension, it would take LESS than 1/2 an hour to fill the tank, so the answer CAN'T be 4/5 of an hour.

If you're going to use this approach, then you would have to MULTIPLY both sides by 4/5....

(5/4 of a tank)(4/5) = (1/2 hour)(4/5)
20/20 of a tank = 4/10 of an hour
1 tank = 2/5 of an hour

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


OK yes! I didn't realise the over-full thing, so yeah that made sense.

But I still didn't understand the logic behind multiplying by 4/5 :/
Expert Post
1 KUDOS received
EMPOWERgmat Instructor
User avatar
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 6909
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 300

Kudos [?]: 2045 [1] , given: 161

Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

Show Tags

New post 30 Dec 2015, 11:16
1
This post received
KUDOS
Expert's post
Hi sarathvr,

The math that you did calculated the time it takes to fill 5/4 of a tank, but the question asks you to fill 4/4 of a tank. Mathematically, since we're dealing with rates, to decrease 5/4 to 4/4 we have to multiply by 4/5. Since we're multiplying one side of the 'equation' by 4/5, we have to multiply the other side by 4/5 also...

(5/4 of a tank)(4/5) = (1/2 hour)(4/5)
20/20 of a tank = 4/10 of an hour
1 tank = 2/5 of an hour

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: A small water pump would take 2 hours to fill an empty tank   [#permalink] 30 Dec 2015, 11:16
    Similar topics Author Replies Last post
Similar
Topics:
5 Experts publish their posts in the topic Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t Bunuel 6 12 Mar 2015, 06:52
4 Experts publish their posts in the topic A group of 3 small pumps and 1 large pump is filling a tank. Each of t jgk 2 01 Nov 2014, 10:39
9 Experts publish their posts in the topic One inlet pipe fills an empty tank in 5 hours. A second inle Bunuel 7 11 Feb 2014, 00:51
5 Experts publish their posts in the topic One water pump can fill half of a certain empty tank in 3 hours. Anoth 36mba 6 04 Jan 2012, 10:17
8 Experts publish their posts in the topic A pump started filling an empty pool with water and continue Jcpenny 6 20 Nov 2008, 11:30
Display posts from previous: Sort by

A small water pump would take 2 hours to fill an empty tank

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


cron

GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.