BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

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.

★★★★★5.0559 reviews
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
Live EA class + 6 months of EA OnDemand
  • Expert-led weekly online sessions
  • EA Masterclass access between classes
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

130-point score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

exponents

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Legendary Member
Posts: 1035
Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member
Thanked: 104 times

by scoobydooby » Sat May 16, 2009 8:09 am
2+2+2^2+2^3+2^4+2^5+2^6+2^7+2^8
=2+(2+2^2+2^3+2^4+2^5+2^6+2^7+2^8)
=2+[sum of GP with common ratio 2, n=8; a(r^n-1)/(r-1)]
=2+2(2^8-1)/(2-1)
=2+2(2^8-1)
=2+2^9-2
=2^9
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Master | Next Rank: 500 Posts
Posts: 435
Joined: Sat Sep 27, 2008 2:02 pmFollowed by: 1 member
Location: San Jose, CA
Thanked: 43 times
GMAT Score:720

by dumb.doofus » Sat May 16, 2009 8:10 am
You just have to apply geometric series here..

2+2+2^2+2^3+2^4+2^5+2^6+2^7+2^8

= 2 + 2 (1+2+2^2+2^3+2^4+2^5+2^6+2^7)

geometric series = a(r^n - 1)/(r-1)
here a = 1, r = 2, n = 8, applying it above gives us

= 2 + 2(2^8 -1)

= 2^9
One love, one blood, one life. You got to do what you should.
https://dreambigdreamhigh.blocked/
https://gmattoughies.blocked/
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 487
Joined: Fri Mar 27, 2009 5:49 am
Thanked: 36 times

Re: exponents

by dtweah » Sat May 16, 2009 8:13 am
kevind147 wrote:from a practice test:

2+2+2^2+2^3+2^4+2^5+2^6+2^7+2^8=?

a. 2^9
b. 2^10
c. 2^16
d. 2^35
e. 2^37

I got e., but the answer is a. Why?
See the pattern:
2+2=4=2^2
2^2+2^2=8=2^3

So continuing this way and inducting on the observed pattern, you will end up with

2^8 +2^8=2^9.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 11
Joined: Wed Mar 18, 2009 8:11 am

by kevind147 » Sat May 16, 2009 8:18 am
scoobydooby wrote:2+2+2^2+2^3+2^4+2^5+2^6+2^7+2^8
=2+(2+2^2+2^3+2^4+2^5+2^6+2^7+2^8)
=2+[sum of GP with common ratio 2, n=8; a(r^n-1)/(r-1)]
=2+2(2^8-1)/(2-1)
=2+2(2^8-1)
=2+2^9-2
=2^9
thanks this makes the most sense to me, but why is the series multiplied by 2? Why is it 2(2^8-1) instead of just (2^8-1)?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1035
Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member
Thanked: 104 times

by scoobydooby » Sat May 16, 2009 8:29 am
that comes from the formula a(r^n-1)/(r-1)

our series: 2+2^2+2^3+2^4+2^5+2^6+2^7+2^8
a=2, r=2, n=8
putting it all in the formula gives 2(2^8-1)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Master | Next Rank: 500 Posts
Posts: 435
Joined: Sat Sep 27, 2008 2:02 pmFollowed by: 1 member
Location: San Jose, CA
Thanked: 43 times
GMAT Score:720

Re: exponents

by dumb.doofus » Sat May 16, 2009 10:29 am
dtweah wrote:
kevind147 wrote:from a practice test:

2+2+2^2+2^3+2^4+2^5+2^6+2^7+2^8=?

a. 2^9
b. 2^10
c. 2^16
d. 2^35
e. 2^37

I got e., but the answer is a. Why?
See the pattern:
2+2=4=2^2
2^2+2^2=8=2^3

So continuing this way and inducting on the observed pattern, you will end up with

2^8 +2^8=2^9.
Nice approach.. quite simple and fast..
One love, one blood, one life. You got to do what you should.
https://dreambigdreamhigh.blocked/
https://gmattoughies.blocked/
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1