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

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Exponents-

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 429
Joined: Wed Sep 19, 2012 11:38 pmFollowed by: 4 members
Thanked: 6 times
by [email protected] » Tue Oct 22, 2013 2:58 am
3 + 3 + 3 + 2 × 3^2 + 2 × 3^3 + 2 × 3^4 + 2 × 3^5 + 2 × 3^6 + 2 × 3^7 =

A. 3^7
B. 3^8
C. 3^14
D. 3^28
E. 3^30

Ans-B
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
Legendary Member
Posts: 1556
Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members
Thanked: 448 times
GMAT Score:650

by theCodeToGMAT » Tue Oct 22, 2013 3:07 am
3 + 2x3^1 + 2 X 3^2 + 2 X 3^3 + 2 X 3^4 + 2 X 3^5 + 2 X 3^6 + 2 X 3^7

3 + 2 ( 3^1 + 3^2 .... 3^7)

3 + 2 ( 3(3^7 - 1)/2) [using GP Sum formula]

3 + 3^8 - 3

3^8
R A H U L
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 429
Joined: Wed Sep 19, 2012 11:38 pmFollowed by: 4 members
Thanked: 6 times

by [email protected] » Tue Oct 22, 2013 3:29 am
:(

Dint get the solution if u take 3+2 as common wnt u keep 1 in its position (within the bracket)? why haven't u added 1?


theCodeToGMAT wrote:3 + 2x3^1 + 2 X 3^2 + 2 X 3^3 + 2 X 3^4 + 2 X 3^5 + 2 X 3^6 + 2 X 3^7

3 + 2 ( 3^1 + 3^2 .... 3^7)

3 + 2 ( 3(3^7 - 1)/2) [using GP Sum formula]

3 + 3^8 - 3

3^8
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 1556
Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members
Thanked: 448 times
GMAT Score:650

by theCodeToGMAT » Tue Oct 22, 2013 3:38 am
Follow the Underlined & Bold Texts

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

3 + 2x3^1 + 2 X 3^2 + 2 X 3^3 + 2 X 3^4 + 2 X 3^5 + 2 X 3^6 + 2 X 3^7

3 + 2x3^1 + 2 X 3^2 + 2 X 3^3 + 2 X 3^4 + 2 X 3^5 + 2 X 3^6 + 2 X 3^7

3 + 2 ( 3^1 + 3^2 .... 3^7) [ GP => 3^1 + 3^2 .... +3^7]

Sum of GP = a(((r^n)-1)/(r-1))

Here, A = 3^1 , r = 3 , n = 7

So, 3 + 2 ( 3(3^7 - 1)/2)

3 + 3^8 - 3

3^8

Is it now better?
R A H U L
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
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 » Tue Oct 22, 2013 4:41 am
[email protected] wrote:3 + 3 + 3 + 2 × 3^2 + 2 × 3^3 + 2 × 3^4 + 2 × 3^5 + 2 × 3^6 + 2 × 3^7 =

A. 3^7
B. 3^8
C. 3^14
D. 3^28
E. 3^30

Ans-B
Always look at the answer choices BEFORE you start to work.
Here, the answer choices are SPREAD OUT.
Thus, we can quickly BALLPARK the correct answer.
Since the greatest term = 2 * 3�, the sum of ALL the terms must be GREATER than 3�.
Eliminate A.

2 * 3� = 2 * 3³ * 3� = 2 * 27 * 81 ≈ 60*80 = 4800.
2 * 3� = (2 * 3�)/3 = 4800/3 = 1600.
2 * 3� = (2 * 3�)/3 ≈ 1600/3 ≈ 500.
The terms to the left of 2 * 3� will be relatively small and thus will have little effect on the final sum.
Thus, the correct answer ≈ 4800+1600+500 = 7000.

Look at the remaining answer choices.
C: 3¹� = 3� * 3� * 3� * 3² = 81*81*81*9 ≈ 80*80*80*10.
Thus, answer choices C, D and E are WAY too big.

The correct answer is B.
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
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 429
Joined: Wed Sep 19, 2012 11:38 pmFollowed by: 4 members
Thanked: 6 times

by [email protected] » Tue Oct 22, 2013 7:13 am
Dint get how u derive this step:

2* 3� = 2 * 3³ * 3� = 2 * 27 * 81 ≈ 60*80 = 4800.
2 * 3� = (2 * 3�)/3 = 4800/3 = 1600.
2 * 3� = (2 * 3�)/3 ≈ 1600/3 ≈ 500.
The terms to the left of 2 * 3� will be relatively small and thus will have little effect on the final sum.



GMATGuruNY wrote:
[email protected] wrote:3 + 3 + 3 + 2 × 3^2 + 2 × 3^3 + 2 × 3^4 + 2 × 3^5 + 2 × 3^6 + 2 × 3^7 =

A. 3^7
B. 3^8
C. 3^14
D. 3^28
E. 3^30

Ans-B
Always look at the answer choices BEFORE you start to work.
Here, the answer choices are SPREAD OUT.
Thus, we can quickly BALLPARK the correct answer.
Since the greatest term = 2 * 3�, the sum of ALL the terms must be GREATER than 3�.
Eliminate A.

2 * 3� = 2 * 3³ * 3� = 2 * 27 * 81 ≈ 60*80 = 4800.
2 * 3� = (2 * 3�)/3 = 4800/3 = 1600.
2 * 3� = (2 * 3�)/3 ≈ 1600/3 ≈ 500.
The terms to the left of 2 * 3� will be relatively small and thus will have little effect on the final sum.
Thus, the correct answer ≈ 4800+1600+500 = 7000.

Look at the remaining answer choices.
C: 3¹� = 3� * 3� * 3� * 3² = 81*81*81*9 ≈ 80*80*80*10.
Thus, answer choices C, D and E are WAY too big.

The correct answer is B.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Tue Oct 22, 2013 12:00 pm
Hi shibsriz,

This question is more about how you "see and organize" your math than about doing calculations.

Here's a quick note before we begin: X + 2X = 3X. Remember this idea (combining like terms) as we work through this question.

3 + 3 + 3 = 9 = 3^2

What's 3^2 + 2(3^2)?.....3(3^2)

What's 3(3^2)? (3^1)(3^2) = 3^3
-------------
What's 3^3 + 2(3^3)?.......3(3^3)

What's 3(3^3)? (3^1)(3^3) = 3^4
------------
What's 3^4 + 2(3^4)?.......3(3^4)

What's 3(3^4)? (3^1)(3^4) = 3^5
-----------
etc.

The final line of this "string" is....

3^7 + 2(3^7) = 3(3^7) = 3^8

Final Answer: B

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1