Last visit was: 19 Jul 2025, 16:59 It is currently 19 Jul 2025, 16:59
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Jul 2025
Posts: 102,627
Own Kudos:
742,792
 [13]
Given Kudos: 98,235
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 102,627
Kudos: 742,792
 [13]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 10 Jun 2016, 01:32
Kudos
Add Kudos
13
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

35% (medium)

Question Stats:

69% (01:50) correct 31% (02:07) wrong based on 475 sessions

History

Date
Time
Result
Not Attempted Yet
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00
ShowHide Answer
Official Answer
C
Most Helpful Reply
User avatar
mohshu
User avatar
Joined: 21 Mar 2016
Last visit: 26 Dec 2019
Posts: 426
Own Kudos:
133
 [6]
Given Kudos: 103
Products:
My Reviews
Posts: 426
Kudos: 133
 [6]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 10 Jun 2016, 04:07
1
Kudos
Add Kudos
5
Bookmarks
Bookmark this Post
Rate of inlet pipe = 1/4
rate of outlet pipe = 1/6

effective rate = 1/4-1/6 = 1/12.
time for total job = 12 hrs but 1/4 of the job already done when pipe was on at 8am,
hence time required to fill the tank = (3/4)*12 = 9hrs.
Option C 18:00
General Discussion
avatar
OptimusPrepJanielle
avatar
Joined: 06 Nov 2014
Last visit: 08 Sep 2017
Posts: 1,779
Own Kudos:
1,449
 [3]
Given Kudos: 23
Expert
Expert reply
Posts: 1,779
Kudos: 1,449
 [3]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 10 Jun 2016, 02:20
3
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00

Assume the total volume of the pool = 24 lts.

Rate of pipe A = 6 lts/hour
Rate of pipe B = 4 lts/hour

Water in the pool at 9 AM = 6 lts.
Rate of filling after 9 AM = 2 lts/hour

Hence the time needed = (24 - 6) /2 = 9 more hours
The pool will be full after 10 hours or at 18:00 hours.

Correct Option: C
User avatar
Mbawarrior01
User avatar
Joined: 12 Oct 2012
Last visit: 23 Jan 2018
Posts: 93
Own Kudos:
358
Given Kudos: 198
WE:General Management (Other)
Posts: 93
Kudos: 358
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 10 Jun 2016, 02:36
Kudos
Add Kudos
Bookmarks
Bookmark this Post
IMO C

Time to fill = Total Job/Combined Rate

Combined Rate = 1/4 - 1/6

Total Job = 3/4 ( As 1/4 is already filled in 1 hour gap)

Thus Time = 9 hours, and ans C.

Please correct if the method is wrong.
avatar
kuksbug
avatar
Joined: 25 Jan 2014
Last visit: 19 Nov 2019
Posts: 25
Own Kudos:
31
 [3]
Given Kudos: 58
Location: India
Concentration: Marketing, Operations
Schools: INSEAD Jan'18 Alberta"19
GMAT 1: 590 Q45 V26
GPA: 3.5
WE:Design (Manufacturing)
Schools: INSEAD Jan'18 Alberta"19
GMAT 1: 590 Q45 V26
Posts: 25
Kudos: 31
 [3]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 13 Jun 2016, 00:36
1
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
Pipe A fills the pool in 4 hrs.
1 hour's work : 1/4

Pipe B empties the pool in 6 hrs.
1 hour's work : 1/6

Together if they work, 1 hour's work = 1/4 -1/6 = 1/12

Given : Pipe A started at 8:00 a.m and Pipe B at 9:00 a.m
Pool filled after 1 hour by Pipe A : 1/4 or 3/12

After 9:00 a.m
Pool filled after 1 hour with both the pipes on : 1/12
Pool filled after 9 hours with both pipes on : 9/12

Pool filled in 1 hour + Pool filled in 9 hours = 3/12 +9/12 =1

Therefore, it takes 10 hrs to fill the pool

As Pipe A started at 8:00 a.m, pool is full at 18:00 hrs

Answer is C.
User avatar
Abhishek009
User avatar
Board of Directors
Joined: 11 Jun 2011
Last visit: 18 Jul 2025
Posts: 5,965
Own Kudos:
5,162
 [1]
Given Kudos: 463
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 5,965
Kudos: 5,162
 [1]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 23 Jun 2017, 08:18
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00

Let capacity of the tank be 12 units..

Efficiency of A = +3 units/hr
Efficiency of B = -2 units/hr
Combined efficiency of A + B is 1 unit/hr

Quote:
If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

In 1 hour pipe A fills up 3 units and 9 units is left
Time required is \(\frac{9}{1} = 9\) hours more

Thus, time required to fill the take is 9 hours after 9 AM , ie 18:00 hours , answer will be (C)
avatar
Arjunarocks
avatar
Joined: 20 Jun 2017
Last visit: 05 May 2018
Posts: 62
Own Kudos:
13
Given Kudos: 12
Location: India
Schools: ISB '20 Georgia Tech '20 (A$) Kelley '20 (A) Marshall '20 (A) Jones '20 (A$) Mendoza '20 (A)
GMAT 1: 720 Q50 V38
GPA: 4
Products:
My Reviews
Schools: ISB '20 Georgia Tech '20 (A$) Kelley '20 (A) Marshall '20 (A) Jones '20 (A$) Mendoza '20 (A)
GMAT 1: 720 Q50 V38
Posts: 62
Kudos: 13
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 25 Jun 2017, 09:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
This is an easy question if done carefully.

so in the first hour, 1/4 of pool is full.
from the next hour (9 am onwards), let it take x hours to fill the pool.

So,

1/4 + (1/4 - 1/6)*x = 1
solving x we get x = 9.

Hence after 9 am it takes 9 hours ie 6 pm or 1800 hours.
User avatar
gracie
User avatar
Joined: 07 Dec 2014
Last visit: 11 Oct 2020
Posts: 1,035
Own Kudos:
1,862
Given Kudos: 27
Posts: 1,035
Kudos: 1,862
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 25 Jun 2017, 12:46
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00

let t=time to fill pool
at 9am pool is 1/6 full
rate of A-B=1/12
t(1/12)=5/6
t=9 hours
9am+9 hours=18:00
C
User avatar
JeffTargetTestPrep
User avatar
Target Test Prep Representative
Joined: 04 Mar 2011
Last visit: 05 Jan 2024
Posts: 2,996
Own Kudos:
7,952
 [1]
Given Kudos: 1,646
Status:Head GMAT Instructor
Affiliations: Target Test Prep
Expert
Expert reply
Posts: 2,996
Kudos: 7,952
 [1]
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 26 Jun 2017, 17:58
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

A. 15:00
B. 17:00
C. 18:00
D. 19:00
E. 20:00

We are given that pipe A fills a swimming pool in 4 hours and pipe B empties the pool in 6 hours. Thus, the fill rate of pipe A is 1/4 and the empty rate of pipe B is 1/6.

Since pipe A was opened at 8 a.m. and pipe B was at 9 a.m., we can let the time of pipe A = t + 1 and the time of pipe B = t. Also, we will subtract the work of pipe B (emptying) from the work done by pipe A (filling) to get the net amount of filling:

(1/4)(t + 1) - (1/6)(t) = 1

t/4 + 1/4 - t/6 = 1

Multiplying by 12, we have:

3t + 3 - 2t = 12

t = 9

So, the pool will be filled at 9 a.m. + 9 hours = 18:00.

Answer: C
User avatar
sasyaharry
User avatar
Joined: 22 Nov 2016
Last visit: 11 Mar 2023
Posts: 199
Own Kudos:
324
Given Kudos: 49
Concentration: Leadership, Strategy
Schools: Wharton Exec '22 (A) Haas EWMBA '23 (A)
Products:
My Reviews
Schools: Wharton Exec '22 (A) Haas EWMBA '23 (A)
Posts: 199
Kudos: 324
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 27 Jun 2017, 14:27
Kudos
Add Kudos
Bookmarks
Bookmark this Post
\(Rate of A = \frac{1}{4}\) and \(Rate of B = \frac{1}{6}\)

Let the W = total work = 1
Pipe A fills 1/4 of the pool in 1 hour. The remaining unfilled portion at 9 am is \(1-\frac{1}{4} = \frac{3}{4}\)

At 9 am pipe B starts emptying the pool. Hence the combined rate is that of \(A-B = \frac{1}{12}\)

We know \(W=\frac{3}{4}\), \(R=\frac{1}{12}\), hence T = 9

Answer is 9 hours from 9 am, i.e 6 PM, C
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 37,451
Own Kudos:
1,013
Posts: 37,451
Kudos: 1,013
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 22 Nov 2022, 20:40
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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.
Moderators:
Bunuel
Math Expert
102627 posts
Krunaal
PS Forum Moderator
698 posts