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

Question from Gmat Prep- Help please! 6

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 68
Joined: Wed Nov 30, 2011 3:12 pm
by bobdylan » Sat Apr 14, 2012 6:26 am
In the arithmetic sequence t1,t2, t3...tn, t1=23 and tn=tn-1 -3 for each n>1. What's the value of n when tn= -4.
a)-1
b)7
c)10
d)14
e)20
Top
Join the discussion
Source: — Problem Solving |
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 » Sat Apr 14, 2012 6:44 am
bobdylan wrote:In the arithmetic sequence t1,t2, t3...tn, t1=23 and tn= t(n-1)-3 for each n>1. What's the value of n when tn= -4.
a)-1
b)7
c)10
d)14
e)20
Since tn= t(n-1)-3, the distance between one value and the next is 3.
Thus, the terms in the sequence are EVENLY SPACED, with an INTERVAL of 3 between successive values.
To count evenly spaced integers, use the following formula:

Number of integers = (biggest-smallest)/interval + 1

In the problem at hand:
Number of integers = (23-(-4))/3 + 1 = 10.
Since there are 10 terms, t(n) = -4 when n=10.

The correct answer is C.
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: 134
Joined: Fri Apr 06, 2012 3:11 amFollowed by: 5 members
Thanked: 35 times

by Shalabh's Quants » Mon Apr 16, 2012 6:01 am
bobdylan wrote:In the arithmetic sequence t1,t2, t3...tn, t1=23 and tn=tn-1 -3 for each n>1. What's the value of n when tn= -4.
a)-1
b)7
c)10
d)14
e)20
For an AP... tn = t1 + (n-1).d; where tn is last term = -4, t1= I term = 23, n = no. of terms, d = common difference = -3.

So, -4 = 23 +(n-1)*-3 => n = 10.
Shalabh Jain,
e-GMAT Instructor
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members
Location: Milpitas, CA
Thanked: 1854 times
GMAT Score:770

by Anurag@Gurome » Mon Apr 16, 2012 6:49 am
bobdylan wrote:In the arithmetic sequence t1,t2, t3...tn, t1=23 and tn=tn-1 -3 for each n>1. What's the value of n when tn= -4.
a)-1
b)7
c)10
d)14
e)20

t(1) = 23 and t(n) = t(n - 1) - 3 for each n > 1

Hence, the series is an arithmetic progression with first term, a = 23 and common difference, d = -3.

Hence, t(n) = a + (n - 1)d = 23 + (n - 1)*(-3) = 23 - 3n + 3 = 26 - 3n

Given that, t(n) = -4
(26 - 3n) = -4
3n = 30
n = 10

The correct answer is C.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Join the discussion
User avatar
Legendary Member
Posts: 626
Joined: Fri Dec 23, 2011 2:50 amFollowed by: 10 members
Location: Ahmedabad
Thanked: 31 times

by ronnie1985 » Mon Apr 16, 2012 7:03 am
(C) QED
Follow your passion, Success as perceived by others shall follow you
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 385
Joined: Mon Apr 16, 2012 8:40 amFollowed by: 29 members
Location: Pune, India
Thanked: 186 times

by aneesh.kg » Mon Apr 16, 2012 9:10 am
Since this is an AP, the difference between tn and tn-1 must be the common difference (d).
Given that tn - tn-1 = -3, therefore d = -3.

(Note that it is an decreasing AP, so it should be no surprise that the given nth term is smaller than the given first term.)

A term at the nth position of an AP, tn = t1 + (n-1).d,
where
t1 = 23 (given)
tn = -4
d = -3

Upon plugging these values in the above expression for tn, we get n = 10.

[C] is the answer.
Top
Join the discussion