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

It is currently 23 Jul 2014, 17:41

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: 04 Jan 2008
Posts: 120
Followers: 2

Kudos [?]: 9 [0], given: 0

Eighty percent of the lights at Hotel California are on at 8 [#permalink] New post 16 Sep 2008, 06:01
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

50% (02:14) correct 50% (01:36) wrong based on 14 sessions
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?

22(2/9)%
16(2/3)%
11(1/9)%
10%
5%
1 KUDOS received
CEO
CEO
User avatar
Joined: 29 Aug 2007
Posts: 2501
Followers: 51

Kudos [?]: 483 [1] , given: 19

GMAT Tests User
Re: Zumit PS 020 [#permalink] New post 16 Sep 2008, 08:13
1
This post received
KUDOS
dancinggeometry wrote:
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?

22(2/9)%
16(2/3)%
11(1/9)%
10%
5%


this kind of the wording is always confusing for me.

a= number of lights supposed to be on
b= number of lights supposed to be off
total = a+b
no of lights that are on = 0.8(a+yb

Light that are supposed to be on but are actually off = 10% of a
Light that are supposed to be on are on = 90% of a

Light that aare supposed to be but are on = 40% of b
Light that aare supposed to be off are off = 60% of b

0.9a + 0.4b = 0.8 (a+b)
a = 4b

Suppose total Lights = 100
so, a = 80 and b = 20

No of lights that are on are on but are supposed to be off = 40% of b = 0.4 (20) = 5

So, the % of lights that are on are supposed to be off = 5/100 = 5%.
//E//
_________________

Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Manager
Manager
avatar
Joined: 22 Jul 2008
Posts: 154
Followers: 1

Kudos [?]: 8 [0], given: 0

Re: Zumit PS 020 [#permalink] New post 16 Sep 2008, 12:35
Let x be the total no. of lights and y be the no. of lights off.
Therefore, (x-y) is the total no. of "on" lights.
Since 40% of lights that should be off are on, 60% of lights that are supposed to be off are actually off. However, 10% of lights that are supposed to be on are off.
Therefore, 60*y/100 + 10*(x-y)/100 = 20*x/100. Solving this gives us x= 5*y. Therefore the no. of lights on are (x-y) = 5y-y = 4y.
Therefore, % of "on" lights that should have been off = {(40y/100) /4y}*100 = 10%
1 KUDOS received
Manager
Manager
avatar
Joined: 25 May 2011
Posts: 164
Followers: 2

Kudos [?]: 34 [1] , given: 71

GMAT Tests User
Re: Zumit PS 020 [#permalink] New post 22 Sep 2011, 14:47
1
This post received
KUDOS
KASSALMD wrote:
Let x be the total no. of lights and y be the no. of lights off.
Therefore, (x-y) is the total no. of "on" lights.
Since 40% of lights that should be off are on, 60% of lights that are supposed to be off are actually off. However, 10% of lights that are supposed to be on are off.
Therefore, 60*y/100 + 10*(x-y)/100 = 20*x/100. Solving this gives us x= 5*y. Therefore the no. of lights on are (x-y) = 5y-y = 4y.
Therefore, % of "on" lights that should have been off = {(40y/100) /4y}*100 = 10%



Agree with you. My approach:

just pick a number (e. 100) for lights.
80 lights are supposed to be on, but 0.1 (that is 8 lights) are off.
20 lights are supposed to be off, but 0.4 (that is 8 lights) are on.

Totally, 80 - 8 + 8=80 lights are on
and the percentage of lights which are on (and not supposed to be on) is 10% (8 out of 80)
Intern
Intern
avatar
Joined: 22 Jun 2008
Posts: 9
Followers: 0

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

Re: Zumit PS 020 [#permalink] New post 22 Sep 2011, 15:44
All this is under the assumption that there are no lights which are neither supposed to be on or off.
Intern
Intern
avatar
Status: Mission MBA
Joined: 02 Jul 2010
Posts: 45
Location: Hyderabad, India
Schools: ISB, IIMs
Followers: 0

Kudos [?]: 8 [0], given: 5

Re: Zumit PS 020 [#permalink] New post 22 Sep 2011, 17:55
shahideh wrote:
KASSALMD wrote:
Let x be the total no. of lights and y be the no. of lights off.
Therefore, (x-y) is the total no. of "on" lights.
Since 40% of lights that should be off are on, 60% of lights that are supposed to be off are actually off. However, 10% of lights that are supposed to be on are off.
Therefore, 60*y/100 + 10*(x-y)/100 = 20*x/100. Solving this gives us x= 5*y. Therefore the no. of lights on are (x-y) = 5y-y = 4y.
Therefore, % of "on" lights that should have been off = {(40y/100) /4y}*100 = 10%



Agree with you. My approach:

just pick a number (e. 100) for lights.
80 lights are supposed to be on, but 0.1 (that is 8 lights) are off.
20 lights are supposed to be off, but 0.4 (that is 8 lights) are on.

Totally, 80 - 8 + 8=80 lights are on
and the percentage of lights which are on (and not supposed to be on) is 10% (8 out of 80)


I really didn't understand why did you pick the numbers 80 and 20?
_________________

If you find my posts useful, Appreciate me with the kudos!! +1

1 KUDOS received
Manager
Manager
avatar
Joined: 25 May 2011
Posts: 164
Followers: 2

Kudos [?]: 34 [1] , given: 71

GMAT Tests User
Re: Zumit PS 020 [#permalink] New post 23 Sep 2011, 03:29
1
This post received
KUDOS
Quote:
I really didn't understand why did you pick the numbers 80 and 20?


when you encounter with a question related to "percentage", it's easier for you to just intellectually pick a number that covers the percentages of the question, and then solve the problem with that number. This approach makes the question tangible.

So, for this question, I pick the number 100 for lights. that is, i suppose the total lights are 100. According to the question, 80% of lights are on at a certain time. So:
80% * 100=80
That is in my approach, 80 lights are on, and 20 other lights, (100-80=20) are off.

In continue, the question says: forty percent of the lights that are supposed to be off are actually on
40% * 20 = 8
That is, 20 lights are supposed to be off, but 8 of them are on now.


again in continue, the question says: ten percent of the lights that are supposed to be on are actually off
10% * 80 = 8
that is, 80 lights are supposed to be on, but 8 lights of them are off now.

so the total number of lights which are on is: 80 + 8 - 8 = 80

To calculate the percentage: (8/80)*100=10

let me know if my explanation is clear : )
Intern
Intern
avatar
Joined: 30 Oct 2011
Posts: 3
Followers: 0

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

Re: Zumit PS 020 [#permalink] New post 03 Nov 2011, 01:27
shahideh wrote:
Quote:
I really didn't understand why did you pick the numbers 80 and 20?


when you encounter with a question related to "percentage", it's easier for you to just intellectually pick a number that covers the percentages of the question, and then solve the problem with that number. This approach makes the question tangible.

So, for this question, I pick the number 100 for lights. that is, i suppose the total lights are 100. According to the question, 80% of lights are on at a certain time. So:
80% * 100=80
That is in my approach, 80 lights are on, and 20 other lights, (100-80=20) are off.

In continue, the question says: forty percent of the lights that are supposed to be off are actually on
40% * 20 = 8
That is, 20 lights are supposed to be off, but 8 of them are on now.


again in continue, the question says: ten percent of the lights that are supposed to be on are actually off
10% * 80 = 8
that is, 80 lights are supposed to be on, but 8 lights of them are off now.

so the total number of lights which are on is: 80 + 8 - 8 = 80

To calculate the percentage: (8/80)*100=10

let me know if my explanation is clear : )



So clear
Manager
Manager
avatar
Joined: 29 Oct 2011
Posts: 189
Concentration: General Management, Technology
Schools: Sloan '16 (D)
GMAT 1: 760 Q49 V44
GPA: 3.76
Followers: 6

Kudos [?]: 67 [0], given: 19

GMAT Tests User
Re: Zumit PS 020 [#permalink] New post 03 Nov 2011, 06:37
My answer is also 10%
Re: Zumit PS 020   [#permalink] 03 Nov 2011, 06:37
    Similar topics Author Replies Last post
Similar
Topics:
1 Eighty percent of the lights at Hotel California are on at 8 krishan 4 08 Nov 2008, 23:02
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®.