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

 It is currently 18 Dec 2018, 09:47

# In Progress:

Admit Calls from Ross Join Chat Room | McCombs Join Chat Room for Latest Updates

### 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

## Events & Promotions

###### Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Happy Christmas 20% Sale! Math Revolution All-In-One Products!

December 20, 2018

December 20, 2018

10:00 PM PST

11:00 PM PST

This is the most inexpensive and attractive price in the market. Get the course now!
• ### Key Strategies to Master GMAT SC

December 22, 2018

December 22, 2018

07:00 AM PST

09:00 AM PST

Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.

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

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 29 Jun 2017
Posts: 467
GPA: 4
WE: Engineering (Transportation)
Re: Eighty percent of the lights at Hotel California are on at 8  [#permalink]

### Show Tags

28 Aug 2017, 08:50
let a% be the lights to be switched on = a %
then lights to be switched off = (100-a) %

total percent of lights switched on is 80. which come on RHS

40% of lights supposed to be off ( 100-a)% are actually on = 0.4(100-a)
also 10% of lights supposed to be on are actually off , so 0.1(a) these are off , so remaining to be on = a - 0.1a

now total lights on = 80
0.4(100-a) + (a-.1a) = 80
a=80 should be on

% of lights supposed to be off are on = 0.4(100-a) / 80 x100
= 0.4x2x100/80
=10%

Ans is D
_________________

Give Kudos for correct answer and/or if you like the solution.

Senior Manager
Joined: 29 Jun 2017
Posts: 467
GPA: 4
WE: Engineering (Transportation)
Eighty percent of the lights at Hotel California are on at 8  [#permalink]

### Show Tags

28 Aug 2017, 09:08
another method:
...........................................act on......................act off
supp on_______________________________________0.1(100-x)___________100-x
supp off_________________ 0.4x_________________0.6x__________________x
__________________________80___________________20___________________100

0.1(100-x) + 0.6x =20
x=20

% = 0.4x/80 *100 = 0.4x20/80 *100 = 10 %
_________________

Give Kudos for correct answer and/or if you like the solution.

Manager
Joined: 31 Jul 2017
Posts: 138
Location: Tajikistan
Concentration: Finance, Economics
Schools: Booth '21, CBS '21
GMAT 1: 690 Q48 V35
GRE 1: Q164 V162
GPA: 3.85
WE: Accounting (Investment Banking)
Re: Eighty percent of the lights at Hotel California are on at 8  [#permalink]

### Show Tags

29 Aug 2018, 08:37
PareshGmat wrote:
Solved using Matrix method. Refer below:

Attachment:
over.png

1. Let the total number of lights = 100

2. 80% of the lights are ON = 80

3. So, lights which are OFF = 100-80 = 20

4. Actual OFF = Suppose OFF = 20

5. 40% of "Suppose OFF" are "Actual ON" $$= \frac{40}{100}* 20 = 8$$

6. Percentage of the lights that are on are supposed to be off $$= \frac{8}{80} * 100 = 10%$$

Bunuel: Kindly update the OA

Also, in the problem, they have used words like "Eighty percent" (instead of 80%) etc.... is this normal in GMAT?

hey,
i dont understand how you got step 4, can you please clarify on it? thanks!
Re: Eighty percent of the lights at Hotel California are on at 8 &nbs [#permalink] 29 Aug 2018, 08:37

Go to page   Previous    1   2   [ 23 posts ]

Display posts from previous: Sort by