NEW HERE? LEARN MORE
closeclose
Last visit was: 11 May 2024, 03:26 It is currently 11 May 2024, 03:26
Decision Tracker
My Rewards
New posts
New comers' posts

Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

If AD is 6, and ADC is a right angle, what is the area of

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
avatar
MackyCee
Manager
Manager
Joined: 17 Dec 2010
Posts: 82
Own Kudos [?]: 37 [1]
Given Kudos: 15
Location: Australia
GMAT 1: 690 Q48 V37
GPA: 3.37
WE:Engineering (Consulting)
Send PM
If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   Updated on: 10 Jul 2014, 04:07
1
Bookmarks
00:00
A
B
C
D
E

Difficulty:

55% (hard)

Question Stats:

56% (01:42) correct 44% (01:47) wrong based on 239 sessions
Hide Show timer Statistics

If AD is 6, and ADC is a right angle, what is the area of triangular region ABC?

(1) Angle ABD = 60°

(2) AC = 12

OPEN DISCUSSION OF THIS QUESTION IS HERE: if-ad-is-6-and-adc-is-a-right-angle-what-is-the-area-of-101200.html
ShowHide Answer
Official Answer
C

Originally posted by MackyCee on 23 Jul 2011, 03:04.
Last edited by Bunuel on 10 Jul 2014, 04:07, edited 2 times in total.
Edited the question.
avatar
MackyCee
Manager
Manager
Joined: 17 Dec 2010
Posts: 82
Own Kudos [?]: 37 [0]
Given Kudos: 15
Location: Australia
GMAT 1: 690 Q48 V37
GPA: 3.37
WE:Engineering (Consulting)
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   23 Jul 2011, 03:14
No matter what I do, I keep getting to "D" - can anyone help me out?

Info from the given:
Based on my understanding of ADC being right, the triangle MUST be isosceles, and triangles ABD and ADC are similar triangles. Is this correct??

Reasoning:
1) Knowing the given of the question, and we know that if angle ABD is 60 degrees => triangle is equilateral, and both triangles are similar triangles (both 30-60-90 triangles).

Knowing the "ratios" of a 30-60-90 triangle, and the dimensions of AD, we can find the value of ANY of the other sides, and hence the area. Sufficient

2) Knowing AD and AC, we can find DC by Pythagoras Theorem, and knowing triangles are similar, we can find the total area. Sufficient.


Can anyone lead me to "C", the OA? Or is the OA wrong?
User avatar
Sudhanshuacharya
Intern
Intern
Joined: 31 May 2011
Posts: 49
Own Kudos [?]: 184 [1]
Given Kudos: 4
Location: India
Concentration: Finance, International Business
GMAT Date: 12-07-2011
GPA: 3.22
WE:Information Technology (Computer Software)
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   23 Jul 2011, 04:33
1
Kudos
MackyCee wrote:
No matter what I do, I keep getting to "D" - can anyone help me out?

Info from the given:
Based on my understanding of ADC being right, the triangle MUST be isosceles, and triangles ABD and ADC are similar triangles. Is this correct??

Reasoning:
1) Knowing the given of the question, and we know that if angle ABD is 60 degrees => triangle is equilateral, and both triangles are similar triangles (both 30-60-90 triangles).

Knowing the "ratios" of a 30-60-90 triangle, and the dimensions of AD, we can find the value of ANY of the other sides, and hence the area. Sufficient

2) Knowing AD and AC, we can find DC by Pythagoras Theorem, and knowing triangles are similar, we can find the total area. Sufficient.


Can anyone lead me to "C", the OA? Or is the OA wrong?


Macky: If the triangle is right angled that does not mean that the triangle is isosceles. I could have been assumed as isosceles only if AD was also bisecting the angle A.

From statement 1 we can only find length of BD. Not sufficient
From statement 2 we can find only the length of DC. Hence not sufficient.

Combining both we get the height and the total base of the triangle, from which we can deduce the area.
avatar
MackyCee
Manager
Manager
Joined: 17 Dec 2010
Posts: 82
Own Kudos [?]: 37 [0]
Given Kudos: 15
Location: Australia
GMAT 1: 690 Q48 V37
GPA: 3.37
WE:Engineering (Consulting)
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   23 Jul 2011, 06:42
Musta been the time of night - but you are definitely 100% correct (as is MGMAT), it doesn't have to be isosceles at all, I must have had my head n the clouds with another concept :S

I need a holiday! haha
User avatar
suraabhi
Intern
Intern
Joined: 08 Feb 2010
Posts: 31
Own Kudos [?]: 13 [1]
Given Kudos: 1
Concentration: Leadership, International Business
Schools: INSEAD Jan '13
GMAT 1: 670 Q50 V31
WE:Project Management (Energy and Utilities)
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   12 Sep 2011, 02:23
1
Bookmarks
Hey,

I also did the mistake but I think MGMAT is right. But this is typical DS question which tricks you with mixed information.

(1) From first you only see one rt angle triangle on the left hand side is 30-60-90 but still do not know anything on the right hand side rt angle triangle

(2) From this statement you know only one side of the base. The point D is not the midpoint. Hence you do know know the lenght of whole base.

(1) & (2) You know the lenght of whole base BD + DC and you have the height given.

Hence C is the right answer.
Please correct me if i am wrong :-)
avatar
subhajeet
Manager
Manager
Joined: 12 Jun 2010
Status:MBA Aspirant
Posts: 79
Own Kudos [?]: 249 [0]
Given Kudos: 1
Location: India
Concentration: Finance, International Business
WE:Information Technology (Investment Banking)
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   17 Sep 2011, 07:18
A realiy tough question. I too made the same mistake... :(
kudos to MGMAT.
avatar
shinna
Intern
Intern
Joined: 03 Jan 2011
Posts: 9
Own Kudos [?]: 8 [0]
Given Kudos: 1
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   17 Sep 2011, 11:11
C is the answer, that was tough! whew! :shock:
avatar
dsmishra1981
Intern
Intern
Joined: 06 Aug 2011
Posts: 3
Own Kudos [?]: 1 [0]
Given Kudos: 2
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   18 Sep 2011, 04:31
C is the answer. It was easy guys, pretty straight forward.

When nothing is given about the figure, one should take only the info that is present in the question.
avatar
unceldolan
Manager
Manager
Joined: 21 Oct 2013
Posts: 154
Own Kudos [?]: 214 [0]
Given Kudos: 19
Location: Germany
Schools: Owen '17 (A$) Sauder '17 (A$) Schulich '17 (WD) Anderson FEMBA '17 (S) McDonough '17 (A) Desautels '17 (S)
GMAT 1: 660 Q45 V36
GPA: 3.51
Send PM
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   10 Jul 2014, 04:05
I don't see how C can be right. If I follow your reasoning, I come to E. (I chose B)

Can anyone explain the calculations?
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 93155
Own Kudos [?]: 622776 [2]
Given Kudos: 81832
Send PM
CAT Tests Forum Quiz Mode
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink] New post   10 Jul 2014, 04:10
1
Kudos
1
Bookmarks
Expert Reply
unceldolan wrote:
I don't see how C can be right. If I follow your reasoning, I come to E. (I chose B)

Can anyone explain the calculations?



If AD is 6 and ADC is a right angle, what is the area of triangular region ABC?

Given: \(AD=6\). Question: \(area_{ABC}=\frac{1}{2}*AD*BC=\frac{1}{2}*6*(BD+DC)=3(BD+DC)=?\)

(1) Angle ABD = 60 --> triangle ABD is 30-60-90 triangle, so the sides are in ratio \(1:\sqrt{3}:2\) --> as AD=6 (larger leg opposite 60 degrees angle) then \(BD=\frac{6}{\sqrt{3}}\) (smallest leg opposite 30 degrees angle). But we still don't know DC. Not sufficient.

(2) AC=12, we can find DC. But we still don't know BD. Not sufficient.

(1)+(2) We know both BD and DC, hence we can find area. Sufficient.

Answer: C.

OPEN DISCUSSION OF THIS QUESTION IS HERE: if-ad-is-6-and-adc-is-a-right-angle-what-is-the-area-of-101200.html
GMAT Club Bot
gmatclubot
Re: If AD is 6, and ADC is a right angle, what is the area of [#permalink]
10 Jul 2014, 04:10
Moderator:
Bunuel
Math Expert
93155 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions