Find all School-related info fast with the new School-Specific MBA Forum

It is currently 25 Jul 2014, 03:49

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Eighty percent of the lights at Hotel California are on at 8

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
User avatar
Joined: 28 Jul 2004
Posts: 136
Location: Melbourne
Schools: Yale SOM, Tuck, Ross, IESE, HEC, Johnson, Booth
Followers: 1

Kudos [?]: 10 [0], given: 2

Eighty percent of the lights at Hotel California are on at 8 [#permalink] New post 08 Nov 2008, 23:02
Eighty percent of the lights at Hotel California are on at 8 p.m. a certain evening. However, forty percent of the lights that are supposed to be off are actually on and ten percent of the lights that are supposed to be on are actually off. What percent of the lights that are on are supposed to be off?

a) 22(2/9)%
b) 16(2/3)%
c) 11(1/9)%
d) 10%
e) 5%
_________________

kris

1 KUDOS received
Intern
Intern
User avatar
Joined: 31 Oct 2008
Posts: 32
Followers: 0

Kudos [?]: 5 [1] , given: 0

Re: Light bulbs ON/OFF [#permalink] New post 09 Nov 2008, 00:55
1
This post received
KUDOS
Oh snap, this one was pretty tricky (if for no other reason than the crazy Sphinxlike wording!) but I got D.

Let T=the total number of lights; F=the number of lights that should be oFF, and N the number of lights that should be oN.
0.8T=0.4F+0.9N
is the mathematical statement of that riddle. Conservation of light bulbs ;) gives us
F+N=T
Substituting one expression into the other, I found
F=0.2T
Returning to the first equation,
0.8T=0.08T+0.9N
So the fraction that should be off is a 10% contribution to the total number on.

You can check out any time you'd like, but you can never leave...
Manager
Manager
User avatar
Joined: 05 Jul 2008
Posts: 139
GMAT 1: Q V
GMAT 2: 740 Q51 V38
Followers: 2

Kudos [?]: 63 [0], given: 40

Re: Light bulbs ON/OFF [#permalink] New post 09 Nov 2008, 05:18
phdizzle wrote:
Oh snap, this one was pretty tricky (if for no other reason than the crazy Sphinxlike wording!) but I got D.

Let T=the total number of lights; F=the number of lights that should be oFF, and N the number of lights that should be oN.
0.8T=0.4F+0.9N
is the mathematical statement of that riddle. Conservation of light bulbs ;) gives us
F+N=T
Substituting one expression into the other, I found
F=0.2T
Returning to the first equation,
0.8T=0.08T+0.9N
So the fraction that should be off is a 10% contribution to the total number on.

You can check out any time you'd like, but you can never leave...


Kudo,
I pick T= 100.
So I have
F+N= 100
0.4F + 0.9N= 80

F=20=>number of the lights that are on are supposed to be off is 20*0.4=8
Manager
Manager
User avatar
Joined: 28 Jul 2004
Posts: 136
Location: Melbourne
Schools: Yale SOM, Tuck, Ross, IESE, HEC, Johnson, Booth
Followers: 1

Kudos [?]: 10 [0], given: 2

Re: Light bulbs ON/OFF [#permalink] New post 10 Nov 2008, 12:06
8 is the correct answer. Thanks a lot guys. I got confused by the wordings of the problem.
_________________

kris

VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1436
Followers: 33

Kudos [?]: 209 [0], given: 1

GMAT Tests User
Re: Light bulbs ON/OFF [#permalink] New post 10 Nov 2008, 17:10
This is a good Q that one won't be able to solve easily using the grid. The simple reason is ON = ! OFF and OFF = !ON

The next tricky thing is to find out that 90% of the lights that are supposed to be on are on and come up with 0.4x+0.9y = 80. the total number of lights that are on are the lights are correctly on and wrongly on.

x+y =100 and we can then solve to get 8

Kudos to phdizzle. Not easy to solve in the heat of the exam.
Re: Light bulbs ON/OFF   [#permalink] 10 Nov 2008, 17:10
    Similar topics Author Replies Last post
Similar
Topics:
1 Eighty percent of the lights at Hotel California are on at 8 dancinggeometry 8 16 Sep 2008, 06:01
Eighty percent of the lights at Hotel California are on at 8 gmatkudi 10 09 Sep 2008, 07:40
Eighty percent of the lights at Hotel California are on at 8 gmatnub 3 25 Jun 2008, 22:24
Eighty percent of the lights at Hotel California are on at 8 Piter 1 23 Aug 2007, 13:10
Eighty percent of the lights at Hotel California are on at 8 iamba 3 16 Jul 2007, 17:06
Display posts from previous: Sort by

Eighty percent of the lights at Hotel California are on at 8

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

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®.