• 7 CATs FREE!
    If you earn 100 Forum Points

    Engage in the Beat The GMAT forums to earn
    100 points for $49 worth of Veritas practice GMATs FREE

    Veritas Prep
    VERITAS PRACTICE GMAT EXAMS
    Earn 10 Points Per Post
    Earn 10 Points Per Thanks
    Earn 10 Points Per Upvote
    REDEEM NOW

Geometry DS question

This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 13
Joined: 01 May 2009
Thanked: 1 times

Geometry DS question

by eyoussef » Mon May 25, 2009 9:55 am
Hello could anyone please help with this one
Image

User avatar
GMAT Instructor
Posts: 99
Joined: 05 Mar 2009
Location: NYC
Thanked: 43 times
Followed by:9 members
GMAT Score:800

by Jose Ferreira » Mon May 25, 2009 11:34 am
This is a great question, and one with a very common GMAT strategy that I espouse to all my students: just start filling in variables for all possible angles, and see what happens.

(I'm going to refer to angles just as the three letters.)

So, for example, is BDC=2x, then we know that BDA=180-2x.

Now, we take that information and apply it to what we know in the triangle to the left:

ADB + DBA + BAD = 180.
(180-2x) + DBA + x = 180
DBA = 180 - x - (180-2x) = x
If DBA= x, and BAD=x, then triangle BAD is isosceles.

Statement one says that segment AD is 6. With our knowledge of isosceles triangles, we then know that BD is also 6. And since the right- hand triangle is isosceles based on the information given, then segment BC must also be 6.

Statement one is sufficient.

Statement two just talks about angles, and gives no information about side lengths.
Jose Ferreira
Founder and CEO, Knewton, Inc.
https://www.knewton.com/gmat

Junior | Next Rank: 30 Posts
Posts: 13
Joined: 01 May 2009
Thanked: 1 times

by eyoussef » Mon May 25, 2009 6:33 pm
now it looks so simple, and I wondering how come I didn't think of that before, thanks :)