GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 24 Apr 2019, 01:08

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

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

M05-09

Author Message
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 54493

Show Tags

16 Sep 2014, 00:24
1
7
00:00

Difficulty:

35% (medium)

Question Stats:

70% (01:45) correct 30% (01:25) wrong based on 149 sessions

HideShow timer Statistics

Water flows into an empty tank of 54 liters via 12 small pipes. The rate of flow in each pipe is 1 liter per hour. However, water also flows out of the tank via several large pipes at the rate of 1.5 liter per hour. If the tank is completely full after 12 hours, how many large pipes are there?

A. 2.5
B. 3
C. 4
D. 5
E. 6

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 54493

Show Tags

16 Sep 2014, 00:24
1
3
Official Solution:

Water flows into an empty tank of 54 liters via 12 small pipes. The rate of flow in each pipe is 1 liter per hour. However, water also flows out of the tank via several large pipes at the rate of 1.5 liter per hour. If the tank is completely full after 12 hours, how many large pipes are there?

A. 2.5
B. 3
C. 4
D. 5
E. 6

The tank is full in 12 hours, therefore, the effective inflow has to be $$\frac{54}{12} = 4.5$$ liters per hour. Currently our nominal inflow is 12 liters per hour and outflow is unknown. To find the outflow, we need to subtract effective inflow from the nominal inflow. $$12 - 4.5 = 7.5$$; We know that each of the large, outgoing pipes has a flow rate of 1.5 liters per hour, therefore, $$\frac{7.5}{1.5} = 5$$.

_________________
Intern
Joined: 09 Feb 2015
Posts: 20

Show Tags

15 May 2015, 02:04
3
Other solutions:
Let x be large pipes:
=> (1*12 - 1.5*x)*12 = 54
Solving we get x=5.
Is it right!
Intern
Joined: 29 May 2015
Posts: 10

Show Tags

25 Aug 2015, 22:17
1
If I may elaborate above explanation,

A = RT
54 = Final R * T
54 = (Inflow Rate - Outflow Rate) * T
54 = (12-1.5x)*12
x=5
Manager
Joined: 25 Mar 2013
Posts: 238
Location: United States
Concentration: Entrepreneurship, Marketing
GPA: 3.5

Show Tags

03 Feb 2017, 09:10
Empowergmat Rich, can you pls explain this simpliest way to solve this problem
What concept am I lacking to think like Bunuel.
_________________
I welcome analysis on my posts and kudo +1 if helpful. It helps me to improve my craft.Thank you
Intern
Joined: 19 Jun 2017
Posts: 11

Show Tags

11 Sep 2017, 19:33
I think this is a poor-quality question and I agree with explanation. Question should explicitly note that the outflow rate of 1.5 l/h is "in each large pipe" (to borrow from the language of the preceding sentence).

Otherwise, Q is excellent as always. But the answer wouldn't make sense if one didn't assume 1.5l/h was on a per pipe basis (of course, one would eventually figure it out, but I don't think question wording should be allowed to unnecessarily cost the user time).
M05-09   [#permalink] 11 Sep 2017, 19:33
Display posts from previous: Sort by

M05-09

Moderators: chetan2u, Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne 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®.