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

Redeem

without (2)?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Legendary Member
Posts: 683
Joined: Tue Jul 22, 2008 1:58 pm
Location: Dubai
Thanked: 73 times
Followed by:2 members

by mals24 » Sun Apr 12, 2009 3:12 am
Let angle ABD = y

Using the exterior angle theorem:
x+y = 2x
y=x

AD = BD = 6

Hence, AD=BD=BC=6

So St 1 is suff.

St 2 just gives you degree measures of the angles and we have no information about any of the lengths of the sides

So st 2 is insuff

For more information on exterior angle theorem check:
https://en.wikipedia.org/wiki/Exterior_angle_theorem
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Sun Apr 12, 2009 7:19 am
Or without using the exterior angle theorem:

-- angle ADB is 180 - 2x, because ADC is a straight line;

-- using that, angle ABD must be x, because the angles in triangle ADB must add to 180.

So triangle ADB is isosceles, and the length of AD is equal to the length of BD, which is equal to BC, since triangle BDC is isosceles. So if AD is 6, so is BC.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Post new topic Post Reply
• Page 1 of 1