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
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
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.

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 559 reviewsTarget Test Prep

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

polygon diagonals

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 234
Joined: Fri Oct 01, 2010 7:28 pmFollowed by: 4 members
Location: chennai
Thanked: 5 times
by pappueshwar » Tue Mar 13, 2012 9:20 am
There is an 8-polygons. what is the number of the diagonals of the 8-polygons ?
A. 20 B. 27 C. 32 D. 43 E. 45


is there any formula for this ?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Quantitative Reasoning |
User avatar
GMAT Instructor
Posts: 509
Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members
Location: Irvine, CA
Thanked: 199 times
GMAT Score:750

by tpr-becky » Tue Mar 13, 2012 11:39 am
when it asks "how many different" they are normally asking for permutations combinations and here that is the case however there is a difference.

First you would solve for the number of combinations of two points out of 8 possible points.
8!/(8-2)!(2!) = 28

However, this accounted for the sides, as a connection between two points that are right next to each other on the shape will form a side, not a diagonal. Therefore you have to subtract the 8 sides from this calculation to get 20

The correct answer is A.

Best of Luck
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 234
Joined: Fri Oct 01, 2010 7:28 pmFollowed by: 4 members
Location: chennai
Thanked: 5 times

by pappueshwar » Tue Mar 13, 2012 7:01 pm
thanks that was awesome
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Thu Mar 15, 2012 8:52 am
pappueshwar wrote:There is an 8-polygons. what is the number of the diagonals of the 8-polygons ?
A. 20 B. 27 C. 32 D. 43 E. 45

is there any formula for this ?
Another approach is to recognize that, for each of the 8 points, there are 5 possible points that we can connect to to create a diagonal.

Aside: there are 5 possible points because we cannot create a diagonal by connecting 2 adjacent points.

These means that there are 40 possible diagonals (8x5=40).
However, we need to recognize that this method counts each diagonal twice. For example, it counts the diagonal AB and the diagonal BA as 2 separate diagonals.

So, to account for this duplication, we'll divide 40 by 2 to get 20[spoiler] (A)[/spoiler]

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1