Last visit was: 19 Sep 2026, 12:14 It is currently 19 Sep 2026, 12:14
Home
Messages
Tests
Schools
Events
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
adkikani
User avatar
IIM School Moderator
Joined: 04 Sep 2016
Last visit: 24 Dec 2023
Posts: 1,215
Own Kudos:
1,371
 [36]
Given Kudos: 1,207
Location: India
WE:Engineering (Other)
Posts: 1,215
Kudos: 1,371
 [36]
Working alone, a small pump takes twice as long as large pump takes to 24 Mar 2018, 03:07
1
Kudos
Add Kudos
35
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
E
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:

79% (01:29) correct 21% (01:44) wrong based on 1350 sessions

History

Date
Time
Result
Not Attempted Yet
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18­
ShowHide Answer
Official Answer
E
Drill more questions that test the same idea in GMAT Club Timed Quiz → Free.
User avatar
niks18
User avatar
Retired Moderator
Joined: 25 Feb 2013
Last visit: 30 Jun 2021
Posts: 859
Own Kudos:
1,830
 [1]
Given Kudos: 54
Location: India
GPA: 3.82
Products:
My Reviews
Posts: 859
Kudos: 1,830
 [1]
Working alone, a small pump takes twice as long as large pump takes to 24 Mar 2018, 03:18
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
adkikani
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank.
Working together at their respective constant rates, the pump can fill the tank in 6 hours.
How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18
Show more

Let Large pump take \(x\) hours to fill the tank. Hence small pump will take \(2x\) hours

Working together the time taken will be \(\frac{2x*x}{(2x+x)}=6 => x=9\)

Hence small pump alone will fill the tank in \(= 2*9=18\) hours

option E
User avatar
Abhishek009
User avatar
Board of Directors
Joined: 11 Jun 2011
Last visit: 17 Dec 2025
Posts: 5,877
Own Kudos:
5,544
 [1]
Given Kudos: 463
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 5,877
Kudos: 5,544
 [1]
Working alone, a small pump takes twice as long as large pump takes to 24 Mar 2018, 07:03
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
adkikani
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank.
Working together at their respective constant rates, the pump can fill the tank in 6 hours.
How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18
Show more
Attachment:
TIME AND EFFICIENCY.PNG
TIME AND EFFICIENCY.PNG [ 1.82 KiB | Viewed 20655 times ]
Time is Inversely related to efficiency (The more the efficiency the lesser the time required)

So, 3e = 18

Or, e = 6 and total work is 18 units

So, Time required for the small pump will be (E) 18 hours.
User avatar
Kinshook
User avatar
Major Poster
Joined: 03 Jun 2019
Last visit: 19 Sep 2026
Posts: 6,134
Own Kudos:
6,112
 [3]
Given Kudos: 164
Location: India
Schools: HBS '28 CBS '26 Wharton '26
GMAT 1: 690 Q50 V34
WE:Engineering (Transportation)
Products:
My Reviews
Schools: HBS '28 CBS '26 Wharton '26
GMAT 1: 690 Q50 V34
Posts: 6,134
Kudos: 6,112
 [3]
Working alone, a small pump takes twice as long as large pump takes to 08 Oct 2019, 08:59
1
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
adkikani
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank.
Working together at their respective constant rates, the pump can fill the tank in 6 hours.
How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18
Show more

1/x + 1/2x = 1/6
3/2x = 1/6
x = 18/2 = 9

2x = 18

IMO E
User avatar
Aboyhasnoname
User avatar
Joined: 19 Jan 2025
Last visit: 09 Sep 2026
Posts: 333
Own Kudos:
111
 [1]
Given Kudos: 63
Products:
My Reviews
Posts: 333
Kudos: 111
 [1]
Working alone, a small pump takes twice as long as large pump takes to 23 Jul 2025, 18:46
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Basically Small machine is doing x part of the work and Large marchine is doing 2x part of the work, if both work the same time...
Now if large machine is removed, the smaller machine would have to do all the 3x part of the work along......
Now...that means ......first it worked for x part for 6 hours...now it has to complete additional 2x parts ... it will take 12 hours...total time alone it will take is 18 hours E

adkikani
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18­
Show more
User avatar
laborumpossimus
User avatar
Joined: 07 Jan 2026
Last visit: 19 Sep 2026
Posts: 103
Own Kudos:
49
Given Kudos: 55
Location: India
Concentration: Marketing, Strategy
Schools: IIM NUS MiM '27 ISB '27
GPA: 3.8
WE:Marketing (Other)
Products:
My Reviews GMAT Club Tests Forum Quiz
Schools: IIM NUS MiM '27 ISB '27
Posts: 103
Kudos: 49
Working alone, a small pump takes twice as long as large pump takes to 07 Sep 2026, 13:52
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I assumed work done to be 60
and made eqn
60/x+60/2x = 6

90=6x
x=15

where am i going wrong
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Sep 2026
Posts: 113,673
Own Kudos:
842,324
 [1]
Given Kudos: 111,668
Products:
GMAT Club Tests
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 113,673
Kudos: 842,324
 [1]
Working alone, a small pump takes twice as long as large pump takes to 07 Sep 2026, 14:24
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18­

Let the large pump take x hours, so the small pump takes 2x hours.

Their combined rate is:

1/x + 1/(2x) = 1/6

3/(2x) = 1/6

18 = 2x

x = 9

So the small pump takes:

2x = 18 hours

Answer: E.

laborumpossimus
I assumed work done to be 60
and made eqn
60/x+60/2x = 6

90=6x
x=15

where am i going wrong
Show more

60/x + 60/(2x) is the combined work rate, in units per hour. So it should equal 60/6 = 10, not 6.

Thus:

60/x + 60/(2x) = 10

which gives x = 9 hours for the large pump, so the small pump takes 18 hours.

Hope this helps.
User avatar
laborumpossimus
User avatar
Joined: 07 Jan 2026
Last visit: 19 Sep 2026
Posts: 103
Own Kudos:
49
Given Kudos: 55
Location: India
Concentration: Marketing, Strategy
Schools: IIM NUS MiM '27 ISB '27
GPA: 3.8
WE:Marketing (Other)
Products:
My Reviews GMAT Club Tests Forum Quiz
Schools: IIM NUS MiM '27 ISB '27
Posts: 103
Kudos: 49
Working alone, a small pump takes twice as long as large pump takes to 07 Sep 2026, 14:30
Kudos
Add Kudos
Bookmarks
Bookmark this Post
i understand now
thank you so much

Bunuel
Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take for the small pump to fill the tank working alone?

A. 8
B. 9
C. 12
D. 15
E. 18­

Let the large pump take x hours, so the small pump takes 2x hours.

Their combined rate is:

1/x + 1/(2x) = 1/6

3/(2x) = 1/6

18 = 2x

x = 9

So the small pump takes:

2x = 18 hours

Answer: E.



60/x + 60/(2x) is the combined work rate, in units per hour. So it should equal 60/6 = 10, not 6.

Thus:

60/x + 60/(2x) = 10

which gives x = 9 hours for the large pump, so the small pump takes 18 hours.

Hope this helps.
Show more
Moderator:
Bunuel
Math Expert
113673 posts