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

It is currently 13 Feb 2016, 08:25
GMAT Club Tests

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

If 2^x - 2^(x-2) = 3(2^13), what is the value of x? A) 9 B)

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
avatar
Joined: 21 Mar 2007
Posts: 73
Followers: 1

Kudos [?]: 51 [0], given: 0

If 2^x - 2^(x-2) = 3(2^13), what is the value of x? A) 9 B) [#permalink] New post 07 Mar 2008, 02:35
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If 2^x - 2^(x-2) = 3(2^13), what is the value of x?
A) 9
B) 11
C) 13
D) 15
E) 17
Senior Manager
Senior Manager
avatar
Joined: 02 Dec 2007
Posts: 456
Followers: 2

Kudos [?]: 105 [0], given: 6

Re: GMAT Prep Explanation please! [#permalink] New post 07 Mar 2008, 05:41
Choice D

2^13( 2^2-1)= 3(2^13)
CEO
CEO
User avatar
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 9

Kudos [?]: 536 [0], given: 4

Re: GMAT Prep Explanation please! [#permalink] New post 07 Mar 2008, 06:11
japped187 wrote:
If 2^x - 2^(x-2) = 3(2^13), what is the value of x?
A) 9
B) 11
C) 13
D) 15
E) 17


d

factor out 2^x and move all variables to one side
_________________

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson

Manager
Manager
avatar
Joined: 21 Mar 2007
Posts: 73
Followers: 1

Kudos [?]: 51 [0], given: 0

Re: GMAT Prep Explanation please! [#permalink] New post 12 Mar 2008, 03:36
Could you please write out the process please!! Thanks!!
CEO
CEO
User avatar
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 9

Kudos [?]: 536 [0], given: 4

Re: GMAT Prep Explanation please! [#permalink] New post 12 Mar 2008, 03:49
see below
Attachments

a.jpg
a.jpg [ 36.43 KiB | Viewed 740 times ]


_________________

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson

CEO
CEO
User avatar
Joined: 29 Mar 2007
Posts: 2584
Followers: 17

Kudos [?]: 304 [0], given: 0

Re: GMAT Prep Explanation please! [#permalink] New post 12 Mar 2008, 06:37
japped187 wrote:
If 2^x - 2^(x-2) = 3(2^13), what is the value of x?
A) 9
B) 11
C) 13
D) 15
E) 17


2^x-2^x/2^2=3(2^13)

2^x(1-1/4)=3(2^13) ---> 2^x(3/2^2)=3(2^13)

cancel the 3's. and multiply the 2^2

thus 2^x=2^15 or x=15

D
Manager
Manager
User avatar
Joined: 05 Feb 2007
Posts: 140
Followers: 1

Kudos [?]: 7 [0], given: 7

Re: GMAT Prep Explanation please! [#permalink] New post 27 Mar 2008, 20:08
bmwhype...thanks for the full answer...but can anyone help me? I'm still confused on this one..
Director
Director
avatar
Joined: 01 May 2007
Posts: 792
Followers: 1

Kudos [?]: 178 [0], given: 0

Re: GMAT Prep Explanation please! [#permalink] New post 28 Mar 2008, 06:57
You could just plug in the answer choices and solve until the right = left side.
Intern
Intern
avatar
Joined: 28 Mar 2008
Posts: 1
Followers: 0

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

Re: GMAT Prep Explanation please! [#permalink] New post 28 Mar 2008, 19:36
japped187 wrote:
If 2^x - 2^(x-2) = 3(2^13), what is the value of x?
A) 9
B) 11
C) 13
D) 15
E) 17



since u need the LHS to come to 3(2^13), start substituting the values for x from the choices given.

first substitute 17 - it becomes 2^17-2^15 = 2^15(2^2 - 1) = 3. 2^15 - which is not what we want

so try the second bigger choice - 15

2^15-2^13 = 2^13( 2^2 - 1) = 3. 2^13 - which is what we want

hence , D is the choice
Director
Director
avatar
Joined: 10 Sep 2007
Posts: 947
Followers: 8

Kudos [?]: 234 [0], given: 0

Re: GMAT Prep Explanation please! [#permalink] New post 28 Mar 2008, 19:42
A much shorter and direct way is following
2^x = 2^2 * 2^(x-2)
So expression in question should read
2^2 * 2^(x-2) - 2^(x-2) = 3(2^13)
2^(x-2)*3 = 3*2^13
=> x-2 = 13
=> x = 15

No need to put values or anything just plain straight forward.
Re: GMAT Prep Explanation please!   [#permalink] 28 Mar 2008, 19:42
Display posts from previous: Sort by

If 2^x - 2^(x-2) = 3(2^13), what is the value of x? A) 9 B)

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| 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®.