Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Exponent Problem

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Thu Aug 26, 2010 12:44 pm
by alicia » Sat Sep 17, 2011 9:21 am
This was a problem on my practice test. Please advise on the step by step solution/breakdown for this problem:

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

The correct answer is d. 15
Top
Join the discussion
Source: — Problem Solving |
Legendary Member
Posts: 1309
Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members
Location: India
Thanked: 310 times
GMAT Score:750

by cans » Sat Sep 17, 2011 9:28 am
2^x - 2^x-2 = 3(2^13)
i think the problem is like this : 2^x - 2^(x-2) = 3(2^13)
-> 2^x - 2^x/4 = 3(2^13) (as 2^(a-b) can be written as 2^a / 2^b)
4* 2^x - 2^x = 3(2^13)*4
3*2^x = 3(2^13)*(2^2)
2^x = 2^(13+2) = 2^15
thus x=15
If my post helped you- let me know by pushing the thanks button ;)

Contact me about long distance tutoring!
[email protected]

Cans!!
Top
Join the discussion
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Thu Aug 26, 2010 12:44 pm

by alicia » Sat Sep 17, 2011 8:03 pm
Thanks!

However, I don't understand how you got from 2^x-2 to 2^x/4

Please explain.
Top
Join the discussion
Legendary Member
Posts: 1309
Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members
Location: India
Thanked: 310 times
GMAT Score:750

by cans » Sat Sep 17, 2011 9:49 pm
2^(x-2) to (2^x)/4
lhs: (2^x)*(2^(-2)) = (2^x)/4
If my post helped you- let me know by pushing the thanks button ;)

Contact me about long distance tutoring!
[email protected]

Cans!!
Top
Join the discussion
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Sun Sep 18, 2011 3:42 am
Can's solution is great. For a less algebraic approach, check here:

https://www.beatthegmat.com/2-x-2-x-2-3- ... tml#309765
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 359
Joined: Wed Mar 11, 2009 4:37 amFollowed by: 2 members
Location: Kolkata, India
Thanked: 50 times

by Abhishek009 » Sun Sep 18, 2011 4:30 am
alicia wrote:This was a problem on my practice test. Please advise on the step by step solution/breakdown for this problem:

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

The correct answer is d. 15
2^x - 2^x-2 = 3(2^13)

Or, 2^x - 2^x-2 = {(2^2) - 1}(2^13)

Or , 2^x - 2^x-2 = 2^15 -2^13


Now we can safely claim x = 15...
Abhishek
Top
Join the discussion
Senior | Next Rank: 100 Posts
Posts: 44
Joined: Sun Aug 21, 2011 1:47 am
Thanked: 3 times

by leumas » Thu Sep 22, 2011 9:31 am
alicia wrote:This was a problem on my practice test. Please advise on the step by step solution/breakdown for this problem:

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

The correct answer is d. 15
There can be only two options. 15 or 17 since rhs has 2^13

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

Substitute 15: Answer will be 4-1 =3 Success!
Top
Join the discussion