Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

A draining pipe can empty a pool in 4 hours

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 366
Joined: Fri Jun 05, 2015 3:35 amFollowed by: 2 members
Thanked: 3 times
by NandishSS » Wed Mar 07, 2018 4:08 am
A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool?

A. 9 liters
B. 18 liters
C. 27 liters
D. 36 liters
E. 45 liters

OA: D[/spoiler]
Top
Join the discussion
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Wed Mar 07, 2018 4:55 am
NandishSS wrote:A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool?

A. 9 liters
B. 18 liters
C. 27 liters
D. 36 liters
E. 45 liters
We can PLUG IN THE ANSWERS, which represent the capacity of the pool.
When the correct answer is plugged in, the time to empty the pool when the draining pipe and intake pipe work simultaneously = 6 hours.
The correct answer is likely to be divisible by the given times and rates (4 hours, 6 hours, 3 liters per hour).
Only D is a multiple of 4, 6 and 3.

D: 36 liters
Since the draining pipe alone takes 4 hours hours to drain the pool, the draining pipe's rate = w/t = 36/4 = 9 liters per hour.
Since the draining pipe REMOVES 9 liters per hour, while the intake pipe ADDS 3 liters per hour, the net removal rate when the two pipes operate together = 9-3 = 6 liters per hour.
Since the two pipes together have a net removal rate of 6 liters per hour, the time for the two pipes together to empty the 36-liter pool = w/r = 36/6 = 6 hours.
Success!

The correct answer is D.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Senior | Next Rank: 100 Posts
Posts: 93
Joined: Tue Dec 16, 2014 9:50 amFollowed by: 4 members
Location: London, UK
Thanked: 2 times
GMAT Score:770

by mbawisdom » Wed Mar 07, 2018 7:35 am
NandishSS wrote:A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool?

A. 9 liters
B. 18 liters
C. 27 liters
D. 36 liters
E. 45 liters

OA: D[/spoiler]
C = Capacity of the pool in L
R = Rate of drainage in L per hour

Work = Rate * Time
(1) C = R *4 (we know that the pool can be emptied in 4 hours)
(2) C + 3*6 = R*6 (we know that when its raining and an extra 3L is added to the pool an hour the pool is emptied in 6 hours

(1) C = 4R
(2) C + 18 = 6R

4R + 18 = 6R [put equation (1) into (2) to eliminate C]
2R = 18
R = 9

C = 4*9 [Put R = 9 into equation (1) to work out C]
C = 36

Answer is D
Top
Join the discussion
User avatar
GMAT Instructor
Posts: 1462
Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members
Location: New York, NY
Thanked: 39 times

by Jeff@TargetTestPrep » Mon Mar 12, 2018 4:09 pm
NandishSS wrote:A draining pipe can empty a pool in 4 hours. On a rainy day, when the pool is full, the draining pipe is opened and the pool is emptied in 6 hours. If rain inflow into the pool is 3 liters per hour, what is the capacity of the pool?

A. 9 liters
B. 18 liters
C. 27 liters
D. 36 liters
E. 45 liters
We can let c = the capacity of the pool. We see that the rate of the pipe emptying the pool is c/4 when the pool is full and it’s not raining. and that the rate of the pipe emptying the pool is c/6 when the pool is full and it’s raining. We can create the following equation:

c/4 - 3 = c/6

Multiplying the equation by 12, we have:

3c - 36 = 2c

c = 36

Answer: D

Jeffrey Miller
Head of GMAT Instruction
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
Top
Join the discussion
Legendary Member
Posts: 2604
Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Tue Mar 13, 2018 9:46 am
Hi NandishSS,

Let the rate of the draining pipe be xx liters per hour. Then the capacity of the tank will be C = time ∗ rate = 4x.

Now, when raining, the net outflow is x-3 liters per hour, and we are told that at this new rate the pool is emptied in 6 hours.

So, the capacity of the pool also equals to C = time ∗ rate = 6(x−3).

Thus we have: 4x = 6(x−3) --> x = 9 --> C = 4x = 36. Option D.

Regards!
Top
Join the discussion