Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 24 Oct 2016, 21:01

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

geometry helppppp

Author Message
Intern
Joined: 06 Oct 2011
Posts: 10
Followers: 0

Kudos [?]: 5 [0], given: 2

Show Tags

08 Aug 2012, 14:07
In the figure below, if AC=12, DC=18, and DB=15, what is the length of AF?

A)8
B)9
C)10
D)11
E)12

Figure reference: http://24.media.tumblr.com/tumblr_m8gfp ... 1_1280.jpg
Senior Manager
Joined: 15 Jun 2010
Posts: 368
Schools: IE'14, ISB'14, Kellogg'15
WE 1: 7 Yrs in Automobile (Commercial Vehicle industry)
Followers: 10

Kudos [?]: 356 [0], given: 50

Show Tags

08 Aug 2012, 15:11
No able to view the link.
Kindly post the question as per rule with OA and in right forum.
_________________

Regards
SD
-----------------------------
Press Kudos if you like my post.
Debrief 610-540-580-710(Long Journey): http://gmatclub.com/forum/from-600-540-580-710-finally-achieved-in-4th-attempt-142456.html

Manager
Joined: 01 Mar 2009
Posts: 194
Location: United States
Concentration: Strategy, Technology
GMAT 1: 660 Q47 V34
GMAT 2: 680 Q46 V38
GPA: 3.2
WE: Consulting (Computer Software)
Followers: 3

Kudos [?]: 42 [0], given: 23

Show Tags

08 Aug 2012, 15:41

I thought this was a very difficult problem. I stared at this for a while before figuring it out. Make point X the point where DB and AF intersect. The angles of the four sided figure in the middle (BCFX), add up to 360. If there are two 90 degree angles, then the remaining angles, FXB and FCB, add up to 180. You will also note that angles FXB and FXD also add up to 180 as well as angles FXB and AXB.

FXB + FCB = 180
FXB + FXD = 180
FXB + AXB = 180

Therefore, Angles FCB, FXD, and AXB are all equal. Lets call their value Y for now. Now you have 3 triangles-- AXB, DXF, AFC, and DBC-- that all have angles that are 90 and Y degrees. They all have the same 3rd angle, which we can call Z for now. We do not need to know the value of Y or Z.

Now, from the above configuration lets extract 2 triangles: CFA and CBD. We can find their proportionality be comparing known values on proportional sides. Since we have values for both CA and CD and they proportional, lets use them. CB:CD = (12):(18) = 2:3. Therefore, the ratio of the sides of triangle CFA to CBD is 2:3. Now lets find AF. Since AF and BD are proportional at 2:3 and BD = 15, then AF = 15(2/3) = 30/3 = 10
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 6966
Location: Pune, India
Followers: 2027

Kudos [?]: 12743 [0], given: 221

Show Tags

09 Aug 2012, 04:40
arifaisal wrote:
In the figure below, if AC=12, DC=18, and DB=15, what is the length of AF?

A)8
B)9
C)10
D)11
E)12

Figure reference: http://24.media.tumblr.com/tumblr_m8gfp ... 1_1280.jpg

Such figures should immediately remind you of similar triangles. The two triangles FCA and BCD have a right angle each and a common angle (angle A) each. Hence, their third corresponding angles would also be equal to each other. By AA rule, the triangles are similar.
Therefore, the ratio of their corresponding sides will be equal.

CA/CD = FA/BD
12/18 = FA/15
FA = 10

_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Re: geometry helppppp   [#permalink] 09 Aug 2012, 04:40
Similar topics Replies Last post
Similar
Topics:
Geometry 5 04 Oct 2013, 11:14
Geometry help 2 22 Jun 2013, 15:00
geometry helppppp 2 17 Aug 2012, 03:56
Geometry Circumference 2 18 Apr 2012, 18:42
Geometry Problem URGENTTTTTT 1 10 Nov 2011, 08:54
Display posts from previous: Sort by