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

Redeem

Isosceles trick

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 14
Joined: Sat Mar 24, 2012 7:52 am
Followed by:1 members

Isosceles trick

by lkcr » Tue Apr 03, 2012 11:38 pm
Not sure if I'm missing something here but...

If triangle RST is an isosceles, what is angle R?
1) angle T = 100
2) angle S = 40

I thought for an isosceles, if you knew the middle angle; [180-middle angle] /2 would be each remaining angle no?

Apparently the answer is NOT choice D....

Sorry I know it sounds like a silly question and it was from the gmatprep as well..
Top
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 61
Joined: Mon Jan 18, 2010 11:09 pm
Thanked: 8 times

by Pharo » Tue Apr 03, 2012 11:49 pm
Statement 1 : If one angle is 100; that means in an isosceles triangle the other angles are 40 each. ;Sufficient

Statement 2 : One angle is 40. Now this is the trick. Since we do not know which sides are equal, we cannot say which angles are equal. If one angle is 40 it might mean:
a. 40-40-100;
b. 40-70-70;
;Hence not sufficient.

--> Answer is A :)
Top

GMAT/MBA Expert

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

by Anurag@Gurome » Tue Apr 03, 2012 11:54 pm
lkcr wrote:Not sure if I'm missing something here but...

If triangle RST is an isosceles, what is angle R?
1) angle T = 100
2) angle S = 40

I thought for an isosceles, if you knew the middle angle; [180-middle angle] /2 would be each remaining angle no?

Apparently the answer is NOT choice D....

Sorry I know it sounds like a silly question and it was from the gmatprep as well..
Triangle RST is an isosceles triangle implies that its two angles are equal.

(1) angle T = 100 implies no other angle can be 100 degrees because the sum of 3 angles in a triangles cannot be more than 180 degrees. This means other two angles, R and S are equal.
So, angle R = (180 - 100)/2 = 80/2 = 40 degrees; SUFFICIENT.

(2) angle S = 40
If angle S = angle R = 40 degrees and angle T = 100 degrees, here angle R = 40 degrees
If angle S = 40 degrees and angle R = angle T = 70 degrees, here angle R = 70 degrees
No definite answer; NOT sufficient.

The correct answer is A.
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
User avatar
Community Manager
Posts: 1060
Joined: Fri May 13, 2011 6:46 am
Location: Utrecht, The Netherlands
Thanked: 318 times
Followed by:52 members

by neelgandham » Wed Apr 04, 2012 12:01 am
If triangle RST is an isosceles, what is angle R?
1) angle T = 100
Angle R + Angle S + Angle T = 180
Case 1: Angle R = Angle T, then
Angle R + Angle T = 200 > 180 (Sum of Angles R,S and T).
Not possible
Case 2: Angle R = Angle S, then
Angle S + Angle S + Angle T = 180
Angle R = Angle S = 40, Angle T = 100
Angle R = Angle S = 40.
Sufficient
2) angle S = 40
Angle R + Angle S + Angle T = 180
Case 1: Angle R = Angle T, then
Angle R + Angle S + Angle R = 180
Angle R = Angle T = 70, Angle S = 40
Case 2: Angle R = Angle S, then
Angle S + Angle S + Angle T = 180
Angle R = Angle S = 40, Angle T = 100
Two different cases, Oops Insufficient!

IMO A
Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/
Top
Post new topic Post Reply
• Page 1 of 1