how to do it fast,

Expert replies

quantskillsgmat: Senior | Next Rank: 100 Posts; Posts: 96; Joined: Fri Apr 23, 2010 1:14 amFollowed by: 1 member; Thanked: 1 times

by quantskillsgmat » Wed Jan 25, 2012 4:03 am

Each side of a polygon is parallol to X axis or Y axis.A corner of this polygon is convex if internal angle is 90 and concave if interior angle is 270 degrees. If the number of convex corners are 25 in this polygon,then concave must be
a)20 b)0 c)21 d)22

Like this post

Source: Beat The GMAT — Problem Solving | Wed Jan 25, 2012 4:03 am

GMAT/MBA Expert

Anurag@Gurome: 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 » Wed Jan 25, 2012 4:10 am

quantskillsgmat wrote:Each side of a polygon is parallol to X axis or Y axis.A corner of this polygon is convex if internal angle is 90 and concave if interior angle is 270 degrees. If the number of convex corners are 25 in this polygon,then concave must be

This can be easily solved without going into much detailed mathematics.

Just note that any polygon such that each of its sides are parallel to parallol to either X axis or Y axis (i.e. all internal angles are either 90 degrees or 270 degrees) will have even number of sides. And hence, even number of corners.

As number of convex corner is ODD, number of concave corners must be EVEN.

Only option C is feasible.

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/

Like this post

mankey: Legendary Member; Posts: 627; Joined: Thu Jun 23, 2011 9:12 amFollowed by: 1 member; Thanked: 4 times

by mankey » Wed Jan 25, 2012 9:09 am

Dear Anurag

Please explain this theorem further, it is still not clear.

Thanks.

Like this post

GMAT/MBA Expert

Anurag@Gurome: 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 » Wed Jan 25, 2012 9:21 am

mankey wrote:Please explain this theorem further...

This is no theorem, just try drawing few polygons for yourself. You'll see that no polygon can be drawn with odd number of sides which will have all the sides parallel to either of the axis.

Refer to the attached figure for better understanding.

Like this post

ArunangsuSahu: Master | Next Rank: 500 Posts; Posts: 382; Joined: Thu Mar 31, 2011 5:47 pm; Thanked: 15 times

by ArunangsuSahu » Wed Jan 25, 2012 11:49 am

@Anurag...This is the formula

25*90+x(-90)=360
x=21

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review