by: adconsectetur
20 mins
by: 2vienna
48 mins
Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Sep 0812:30 AM EDT
-01:30 AM EDT
Looking for your GMAT motivation to break through the score plateau? Pragati improved her score by massive 160 points with strategic guidance and hard-work! Find out how personalized mentorship and a strong mindset can turn GMAT struggles into success.
Sep 1001:00 AM EDT
-02:00 AM EDT
Learn how Keshav, a Chartered Accountant, scored an impressive 705 on GMAT in just 30 days with GMATWhiz's expert guidance. In this video, he shares preparation tips and strategies that worked for him, including the mock, time management, and more.
Sep 1008:00 PM PDT
-09:00 PM PDT
Free- full-length test + 15 concept videos + 150+ short videos + study plan!
Sep 1507:00 PM EDT
-09:00 PM EST
Elite scores are possible when you enroll in a powerful GMAT course, taught live online + 6 months access to TTP OnDemand video courses included! Class starts Tues/Thurs Sept. 15, 2026 - Nov. 15, 2027, 7:00pm-9:00pm EST
Sep 2107:00 PM EDT
-10:00 PM EDT
Boost your GMAT score in less than one month in a live online class + 6 months access to TTP OnDemand video courses included! Class starts Mon, Tues, Wed, Thur, Fri Sept. 21, 2026 - Oct. 9, 2027, 7:00pm-10:00pm EST
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
83% (02:16) correct
17%
(02:38)
wrong
based on 4556
sessions
History
Date
Time
Result
Not Attempted Yet
Two water pumps, working simultaneously at their respective constant rates, took exactly four hours to fill a certain swimming pool. If the constant rate of one pump was 1.5 times the constant rate of the other, how many hours would it have taken the faster pump to fill the pool if it had worked alone at it's constant rate?
A. 5
B. 16/3
C. 11/2
D. 6
E. 20/3
A. 5
B. 16/3
C. 11/2
D. 6
E. 20/3
Work rate problems are my weakest area. For whatever reason I get mixed up on these problem. Even knowing the answer to this question I can't figure out how it comes out to that answer. Any help would be great, thanks!
If this question felt shaky,
try an adaptive mini quiz of similar problems in
GMAT Club Forum Quiz →. Free plan gives 5 questions per day.
kmasonbx
Say the rate of the faster pump is x pool/hour, then the rate of the slower pump would be x/1.5=2x/3 pool/hour.
Since, the combined rate is 1/4 pool/hour, then we have that x+2x/3=1/4 --> x=3/20 pool hour.
The time is reciprocal of the rate, therefore it would take 20/3 hours the faster pump to fill the pool working alone.
Answer: E.
Theory on work/rate problems: work-word-problems-made-easy-87357.html
All DS work/rate problems to practice: search.php?search_id=tag&tag_id=46
All PS work/rate problems to practice: search.php?search_id=tag&tag_id=66
All DS work/rate problems to practice: search.php?search_id=tag&tag_id=46
All PS work/rate problems to practice: search.php?search_id=tag&tag_id=66
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
Kimberly77
Two water pumps, working simultaneously at their respective constant rates, took exactly four hours to fill a certain swimming pool. If the constant rate of one pump was 1.5 times the constant rate of the other, how many hours would it have taken the faster pump to fill the pool if it had worked alone at it's constant rate?
A. 5
B. 16/3
C. 11/2
D. 6
E. 20/3
APPROACH 1:
If you assume that the RATE of the faster pump is x pool/hour, then the RATE of the slower pump would be x/1.5 = 2x/3 pool/hour.
Since the combined rate is 1/4 pool/hour, then we have that x + 2x/3 = 1/4 --> x = 3/20 pool/hour.
The time is the reciprocal of the rate, therefore it would take 20/3 hours for the faster pump to fill the pool working alone.
Answer: E.
APPROACH 2:
If you assume that the RATE of the slower pump is x pool/hour, then the RATE of the faster pump would be 1.5x = 3x/2 pool/hour.
Since the combined rate is 1/4 pool/hour, then we have that x + 3x/2 = 1/4 --> x = 1/10 pool/hour. The RATE of the faster pump would be 3x/2 = 3/20 pool/hour.
The time is the reciprocal of the rate, therefore it would take 20/3 hours for the faster pump to fill the pool working alone.
Answer: E.
APPROACH 3:
If you assume that the TIME it takes for the slower pump to fill the pool is x hours, then the TIME it takes for the faster pump to fill the pool would be x/1.5 = 2x/3 hours. Consequently, the rates of the slower and faster pumps would be 1/x and 3/(2x) pool/hour respectively.
Since the combined rate is 1/4 pool/hour, then we have that 1/x + 3/(2x) = 1/4 --> x = 10 hours. The TIME it takes for the faster pump to fill the pool would be x/1.5 = 2x/3 = 20/3 hours.
Answer: E.
APPROACH 4:
If you assume that the TIME it takes for the faster pump to fill the pool is x hours, then the TIME it takes for the slower pump to fill the pool would be 1.5x = 3x/2 hours. Consequently, the rates of the faster and slower pumps would be 1/x and 2/(3x) pool/hour respectively.
Since the combined rate is 1/4 pool/hour, then we have that 1/x + 2/(3x) = 1/4 --> x = 20/3 hours.
Answer: E.
As you can see, you can denote x as either the rate or the time of the slower or faster pump. It will still yield the same answer.
Hope it helps.
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
General Discussion
AMITAGARWAL2
Joined: 06 Jul 2013
Last visit: 08 May 2014
Posts: 71
Schools: McCombs PT '16 Jones '16
GMAT 1: 620 Q48 V28
GMAT 2: 700 Q50 V33
Products:
i am little confused. If i take slower pump as X then 1/X + 1/1.5X = 1/4 which would result X = 20/3 and so faster pump as 10..... where i am going wrong...
AMITAGARWAL2
In my solution x is the rate in your solution x is the time.
In your solution x is the time of the faster pump and 1.5x is the time of the slower pump (faster pump needs less time).
Hope it's clear.
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
kmasonbx
sol:
Rates be A and B
(A+B) * Time = Work
(A+B) * 4 = 1 ---->eq 1
A= 3B/2 ----->eq 2
substituting eq 2 in eq 1
B = 1/10 --->eq 3
substituting eq 3 in eq 2
A= 3/20
Time= work/rate
= 1/(3/20) =>20/3
I did,
A+B = 4
A = 1.5B
4-B = 1.5B => B = 8/5
Why is this wrong?
A+B = 4
A = 1.5B
4-B = 1.5B => B = 8/5
Why is this wrong?
Skag55
We are told that "two water pumps, working simultaneously at their respective constant rates, took exactly four hours to fill a certain swimming pool".
If one pump needs A hours to fill the pool (rate=1/A) and another need B hours to fill the same pool (rate=1/B), then 1/A + 1/B = 1/4.
Solving 1/A + 1/B = 1/4 and A = 1.5B gives A=10 and B=20/3.
Check the links provided here: two-water-pumps-working-simultaneously-at-their-respective-155865.html#p1245761 for more.
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
AMITAGARWAL2
Let me elaborate the math so that it's absolutely clear:
Let's calculate the combined rate first:
Rate x Time = Work
Rate x 4 = 1 [It takes 4 hours for both the pumps to fill up the pool]
Rate = 1/4 [So, 1/4 is the rate for the pumps working together]
Now, the let's assume the rate for the slower pump is x ; so the rate for the faster pump will be 1.5x
According to our previous calculations,
Slower pump + faster pump = 1/4
x + 1.5x = 1/4
2.5x = 1/4
x = 1/10 [slower pump's rate]
so, the faster pump's rate is 1/10 x 1.5 = 3/20
Now let's calculate the time it will take for the faster pump
Rate x Time = Work
3/20 x Time = 1
Time = 1 x 20/3 = 20/3 the answer
kmasonbx
fast pump takes x hour
Slow pump takes 1.5x hour
so
1/x+1/1.5x = 1/4
> (1.5+1)/1.5x = 1/4
> 2.5/1.5x = 1/4
> 1.5 x = 10
>x = 10/1.5
>x = 20/3
Somebody confirm whether this is a right approach to do this type of problem or not. Thanks
xLUCAJx
Joined: 22 Apr 2015
Last visit: 11 Jul 2026
Posts: 37
Location: United States
Schools: Ross Evening MBA"20 (A)
GMAT 1: 620 Q46 V27
GPA: 3.86
How would you solve this problem by saying the faster pump 1.5x and slower x. I cant seem to figure that out.
Abhishek009
Board of Directors
Joined: 11 Jun 2011
Last visit: 17 Dec 2025
Posts: 5,881
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 5,881
xLUCAJx
Plug in some values-
Attachment:
Plug in.PNG [ 2 KiB | Viewed 119036 times ]
Quote:
Capacity of the swimming pool is -
5*4 = 20
Quote:
The faster pump is pump B, so time required by fill the swimming pool alone will be = Total Capacity of the pool/Efficiency of Pipe B
20/3
Hence answer is (E)
_________________
JeffTargetTestPrep
Expert
Target Test Prep Representative
Joined: 04 Mar 2011
Last visit: 05 Jan 2024
Posts: 2,973
Status:Head GMAT Instructor
Affiliations: Target Test Prep
Expert reply
Posts: 2,973
kmasonbx
We are given that the rate of 1 pump is 1.5 times faster than the rate of the other pump. Since 1 pool is being filled and rate = work/time, the rate of the faster pump is 1/x, in which x = the time it takes for the faster pump to fill the pool, and the rate of the slower pump = 1/(1.5x) = 1/(3x/2) = 2/3x.
Since when the pumps work together they take 4 hours to fill 1 pool, we can create the following equation:
work of faster pump + work of slower pump = 1
(1/x)4 + (2/3x)4 = 1
4/x + 8/3x = 1
Multiplying the entire equation by 3x, we have:
12 + 8 = 3x
20 = 3x
20/3 = x
Answer: E
_________________
Jeffrey Miller | Head of GMAT Instruction |
[email protected]
See why Target Test Prep is the top rated GMAT course on GMAT Club. Read Our Reviews
Bunuel
I'm having trouble seeing how you got x= 3/20 from x+2x = 1/4. Do you mind showing step by step? thank you!!
rnz
\(x+\frac{2x}{3}=\frac{1}{4}\);
\(\frac{3x+2x}{3}=\frac{1}{4}\);
\(\frac{5x}{3}=\frac{1}{4}\);
\(20x=3\);
\(x=\frac{3}{20}\).
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
EMPOWERgmatRichC
Expert
Major Poster
Joined: 19 Dec 2014
Last visit: 31 Dec 2023
Posts: 21,775
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Expert reply
Hi All,
This is an example of a Work Formula question. Any time you have two entities (people, machines, water pumps, etc.) working on a job together, you can use the following formula:
(AB)/(A+B) = Total time to do the job together
Here, we're told that the total time = 4 hours and that one machine's rate is 1.5 times the other machine's rate…
If B = 1.5A then we have…
(A)(1.5A)/(A + 1.5A) = 4
1.5(A^2)/2.5A = 4
(3/2)(A^2) = 10A
A^2 = 20A/3
A = 20/3 hours to fill the pool alone
Final Answer:
GMAT assassins aren't born, they're made,
Rich
This is an example of a Work Formula question. Any time you have two entities (people, machines, water pumps, etc.) working on a job together, you can use the following formula:
(AB)/(A+B) = Total time to do the job together
Here, we're told that the total time = 4 hours and that one machine's rate is 1.5 times the other machine's rate…
If B = 1.5A then we have…
(A)(1.5A)/(A + 1.5A) = 4
1.5(A^2)/2.5A = 4
(3/2)(A^2) = 10A
A^2 = 20A/3
A = 20/3 hours to fill the pool alone
Final Answer:
GMAT assassins aren't born, they're made,
Rich
Posts: 292
kmasonbx
Drawing a chart:
Since they are working together we add rates:
One pump has a rate of 1 and the other 3/2, together their t=4
so combined 2/2+3/2 * 4 = 20/2 = 10
together they do 10 units of work
To find the individual time we divide total work by individual rate
so 10/(3/2) = 20/3, E
Or...
1/1r + 1/(3/2r) = 1/4
1r+(3/2r) / (3/2)r^2 = 1/4
(3/2)r^2 / (2/2)r+(3/2r) = 4
(3/2)r / (5/2) = 4
(3/5)r = 4
r = 4*(5/3) = 20/3
I read quite a few solutions and they all have the following equation set up: 1/x+1/1.5x=1/4. But I have 1/x+1/1.5x=4. I don't understand why "x" is time. "x" to me is rate because the question states "constant rate of one pump was 1.5 times the constant rate of the other".
Can Bunuel or someone else please help? Thanks!
Can Bunuel or someone else please help? Thanks!
Irising
x is an unknown and you can denote by x either time or rate, it's your choice. Doesn't really matter.
If you say x is the rate, then you get: x + 2x/3 = 1/4. My solution here uses x as the rate: https://gmatclub.com/forum/two-water-pu ... l#p1245761
If you say x is the time, then you get: 1/x + 2/(3x) = 1/4.
In any case notice that we sum the rates.
_________________
New to the GMAT Club?
- • Questions: Question Bank | Bunuel's Signature Collection
• Tests: GMAT Club Tests | Forum Quiz
• Guides: Quantitative | Critical Reasoning | Reading Comprehension | Ultimate Quant Guide | All You Need for Quant
• Rules: Quantitative | Verbal
Bunuel
Thank you for your reply! Please bare with me as I am still trying to understand the problem. When you say "we sum rates", do you also imply that we cannot sum time? In my equation, I set x as rate. Then I thought 1/x must be time (work/rate=time). And based on that, I sum time to solve for x: 1/x+1/(1.5x)=4, time of the slow pump+time of the fast pump=total time. There must be something wrong with my logic here but I can't seem to figure it out.
Moderator:
Announcements
How to Tell If Your GMAT Prep Resources Are Actually Helping You
Subscribe to GMAT Club for New Podcast Episodes, Debriefs, & Insightful Sessions on GMAT Preparation
Subscribe to GMAT Club for New Podcast Episodes, Debriefs, & Insightful Sessions on GMAT Preparation
Tuck at Dartmouth
AI at Dartmouth Tuck: How the School Is Preparing Leaders for the Age of Artificial Intelligence
Inside the courses, research, and hands-on learning defining wise, decisive leadership in an AI-driven world.
Read More
Inside the courses, research, and hands-on learning defining wise, decisive leadership in an AI-driven world.
Read More
Top 5 GMAT Debrief Videos
Success stories and strategies from high-scoring candidates.