Author 
Message 
TAGS:

Hide Tags

Board of Directors
Joined: 17 Jul 2014
Posts: 2754
Location: United States (IL)
Concentration: Finance, Economics
GPA: 3.92
WE: General Management (Transportation)

D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
03 Oct 2014, 15:05
9
This post was BOOKMARKED
Question Stats:
45% (02:21) correct 55% (02:25) wrong based on 161 sessions
HideShow timer Statistics
D, E and F are points on the sides of triangle ABC above, such that quadrilateral AEFD is a rectangle. If DC=1, and CF=4, what is the value of AD? (1) 3EB = AB (2) FB = 2 Attachment:
DS.jpg [ 13.2 KiB  Viewed 3625 times ]
Official Answer and Stats are available only to registered users. Register/ Login.
Last edited by Bunuel on 12 Sep 2016, 04:40, edited 2 times in total.
Renamed the topic, edited the question and added the OA.



Board of Directors
Joined: 17 Jul 2014
Posts: 2754
Location: United States (IL)
Concentration: Finance, Economics
GPA: 3.92
WE: General Management (Transportation)

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
03 Oct 2014, 15:09
since <FDA=90 we can conclude that <CDF=90 knowing CD & CF, we can find DF
in order to find AD, we need to know AE & EB (1) we can find AE & AB since DF = AE. but we cannot find FB (2) does not tell us anything about AB
1+2 can solve for DA answer C
am I right?



Manager
Joined: 21 Sep 2012
Posts: 218
Location: United States
Concentration: Finance, Economics
GPA: 4
WE: General Management (Consumer Products)

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
04 Oct 2014, 01:02
Given : DC=1 and CF=4 AEFD is a rectangle.
DF=(4^21^2)^1/2 DF=(161)^1/2 DF=15^1/2 Therefore AE=15^1/2... AEFD is a rectangle
Statement 1 : 3EB = AB Therefore, AE=AB*2/3 AB=3AE/2 AB=(3*15^1/2)/2 Therefore EB=(15^1/2)/2
Let AD be x. Therefore FE=x using Pythagoras,
AC^2+AB^2=BC^2 (1+x)^2+[(3*15^1/2)/2]^2=(4+FB)^2 ..............1
Length of FB can be derived in terms of x using Pythagoras. FB^2=[(15^1/2)/2]^2 +x^2 So equation 1 can be solved to get value of x.
statement is sufficient.
statement 2 : FB = 2
BC= CF+FB BC=4+2 BC=6
Let AD be x, therefore FE=x (AEFD is a rectangle)
using Pythagoras, AC^2+AB^2=BC^2 (1+x)^2+[(15^1/2)/2+EB]^2= 6^2 .............. 1
EB can be derived in terms of x using Pythagoras EB^2= FB^2FE^2 EB^2= 2^2x^2 Value of EB^2 can be put in equation 1 and value of x can be obtained.
Statement is sufficient.
Ans  D



Tutor
Joined: 20 Apr 2012
Posts: 100
Location: Ukraine
GMAT 1: 690 Q51 V31 GMAT 2: 730 Q51 V38
WE: Education (Education)

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
04 Oct 2014, 13:41
4
This post received KUDOS
4
This post was BOOKMARKED
mvictor wrote: D, E and F are points on the sides of triangle ABC above, such that quadrilateral AEFD is a rectangle. If DC=1, and CF=4, what is the value of AD? (1) 3EB = AB (2) FB = 2 It is very easy to solve if you mention two similar triangles. Triangle CDF is similar to FEB since angle D=angle E=90 degrees angle DFC=angle EBF since DFAB. Because of similarity the corresponding sides of triangles must be proportional. Our task is to find such ratio. (1) Sufficient. Here we know that proportional coefficient is 2, since DF=AE=ABEB=3EBEB=2EB. Each side in triangle CDF must be twice the corresponding side of triangle FEB. Therefore, AD=FE=1/2 (2) Sufficietnt CF=4, FB=2, hence proportional coefficient is 2. Each side in triangle CDF must be twice the corresponding side of triangle FEB. Therefore, AD=FE=1/2. The correct answer is D.
_________________
I'm happy, if I make math for you slightly clearer And yes, I like kudos:)



Veritas Prep GMAT Instructor
Joined: 23 Oct 2013
Posts: 144

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
17 May 2015, 18:44
With data sufficiency questions, particularly geometry ones, you always want to make as many inferences as you can upfront. We can see that triangle CDF is a right triangle, because using the supplementary angle rule we know that angle CDF is 90 degrees. When they give us that leg DC = 1 and hypotenuse CF = 4 then, we can use the formula a^2 + b^2 = c^2 to see that leg DF = sqrt15. Because AEFD is a rectangle, AE must also be sqrt15. Statement 1 tells us that 3EB = AB, and therefore we know that EB = AB/2. Using the supplementary angle rule again we see that angle FEB is a 90 degree angle, and therefore triangle FEB is also a right triangle. Statement 2 gives us the hypotenuse of this triangle, and because we already have the information for leg EB (its sqrt15/2), we know that we can find the other leg EF. Again using the fact that AEFD is a rectangle, we know that EF will equal AD, and therefore with both statements together we can find AD, yielding answer choice C. We of course would not do the actual math, because all we want to prove is sufficiency. I hope this helps!
_________________
Brandon Veritas Prep  GMAT Instructor
If you found this post helpful, please give me kudos!!!
Save $100 on Veritas Prep GMAT Courses And Admissions Consulting Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.
Veritas Prep Reviews



Manager
Joined: 08 Oct 2013
Posts: 51

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
28 May 2015, 18:51
So the OA is C or D ?. I Got C...
Regards, Aj



eGMAT Representative
Joined: 04 Jan 2015
Posts: 886

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
29 May 2015, 01:26
AjChakravarthy wrote: So the OA is C or D ?. I Got C...
Regards, Aj Dear AjChakravarthyThe correct answer is D. Here's an easy solution for this question. Let the length of AD be x. First of all, let's represent the given information on the diagram. By applying Pythagoras Theorem on right Triangle CDF, we can see that DF = \(\sqrt{15}\). Since opposite sides of a rectangle are equal, AE = \(\sqrt{15}\). Analyzing Statement 13EB = ABThis means, EB = \(\frac{AB}{3}\) Now, AB = AE + EB So, AB = \(\sqrt{15} +\frac{AB}{3}\). Upon solving this equation, we get \(AB = \frac{3√15}{2}\) Now, in right triangle CAB, \(tanC = \frac{AB}{AC} = \frac{3√15}{2(1+x)}\) . . . (1) In right triangle CDF, \(tanC = \frac{DF}{CD} =\frac{√15}{1}\) . . . (2) Upon equating (1) and (2) and solving for x, we get x = 1/2 So, St. 1 alone is sufficient to determine a unique value of x. Analyzing Statement 2FB = 2This means, BC = 4 + 2 = 6 in right triangle CAB, \(cosC = \frac{AC}{BC} = \frac{(1+x)}{6}\) . . . (1) In right triangle CDF, \(cosC = \frac{CD}{CF} =\frac{1}{4}\) . . . (2) Upon equating (1) and (2) and solving for x, we get x = 1/2 So, St. 2 alone is sufficient to determine a unique value of x. Hope this helped! Best Regards Japinder
_________________
 '4 out of Top 5' Instructors on gmatclub  70 point improvement guarantee  www.egmat.com



Intern
Joined: 01 Apr 2016
Posts: 11

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
13 Jul 2016, 07:19
My answer with THALES
Attachments
20160713 16.15.26.jpg [ 190.48 KiB  Viewed 1281 times ]
20160713 16.14.31.jpg [ 118.59 KiB  Viewed 1281 times ]



NonHuman User
Joined: 09 Sep 2013
Posts: 6557

Re: D, E and F are points on the sides of triangle ABC above, such that qu [#permalink]
Show Tags
05 Jan 2018, 12:04
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: D, E and F are points on the sides of triangle ABC above, such that qu
[#permalink]
05 Jan 2018, 12:04






