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

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Is side BC parallel to DE ?

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times
by goelmohit2002 » Sat Sep 12, 2009 10:13 pm
In triangle ABC, D is a point on side AB. E is a point on side AC. Is DE parallel to BC ?

a) D is midpoint of AB.
b) E is midpoint of AC.

OA after some discussion.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sun Jun 21, 2009 10:25 am
Location: Germany
Thanked: 7 times

by Nermal » Sun Sep 13, 2009 2:22 am
IMO C
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times

by goelmohit2002 » Sun Sep 13, 2009 3:21 am
Nermal wrote:IMO C
Can you please give your reasoning for the same ?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1035
Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member
Thanked: 104 times

by scoobydooby » Sun Sep 13, 2009 9:44 am
comes from the mid-point theorem of triangles: a line joining the midpoints of a triangle is parallel to the third side and is half the length of the 3rd side.
Last edited by scoobydooby on Sun Sep 13, 2009 10:52 am, edited 2 times in total.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sun Jun 21, 2009 10:25 am
Location: Germany
Thanked: 7 times

by Nermal » Sun Sep 13, 2009 10:37 am
scoobydooby wrote:we need niether of the options. it follows from the stem itself that DE is parallel to BC and is equal to 1/2 BC

comes from the mid-point theorem of triangles: a line joining the midpoints of a triangle is parallel to the third side and is half the length of the 3rd side.
Of course we need both of the statements since the question stem only tells us that the points E and D lie somewhere on the respective sides of the triangle.
The statements tell us that both of the points are the midpoints of the sides. Without that information we cannot solve this problem at all!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1035
Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member
Thanked: 104 times

by scoobydooby » Sun Sep 13, 2009 10:47 am
oops, you are right nermal. i was careless enough to read "points' as "mid-points'. my bad!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times

by goelmohit2002 » Sun Sep 13, 2009 10:07 pm
Thanks. But can you pkease prove this theorem mathematically....i tried proving the same using similar triangles concept...but was not able to do so....
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: Tue Mar 31, 2009 3:40 am
GMAT Score:650

Re: Is side BC parallel to DE ?

by euwe » Mon Sep 14, 2009 12:38 am
goelmohit2002 wrote:In triangle ABC, D is a point on side AB. E is a point on side AC. Is DE parallel to BC ?

a) D is midpoint of AB.
b) E is midpoint of AC.

OA after some discussion.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sun Jun 21, 2009 10:25 am
Location: Germany
Thanked: 7 times

by Nermal » Mon Sep 14, 2009 2:42 am
I thought my my way through this problem and looked for a mathematical reasoning afterwards.
What I found was the so called RAR-rule of similar triangles.
It says that triangles are similar (similar meaning having the same measures of angles but different side lenghts) when one angle is the same (here: angle at vertex A) and the sides that contain this angle are in the same ratio (here: AE=(1/2)AC and AD=(1/2)AB).
Therefore the other angles are the same as well and this can only be true if the sides CB and DE are parallel.

Look here: https://www.onlinemathlearning.com/simil ... ngles.html
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times

by goelmohit2002 » Mon Sep 14, 2009 11:42 am
Nermal wrote:I thought my my way through this problem and looked for a mathematical reasoning afterwards.
What I found was the so called RAR-rule of similar triangles.
It says that triangles are similar (similar meaning having the same measures of angles but different side lenghts) when one angle is the same (here: angle at vertex A) and the sides that contain this angle are in the same ratio (here: AE=(1/2)AC and AD=(1/2)AB).
Therefore the other angles are the same as well and this can only be true if the sides CB and DE are parallel.

Look here: https://www.onlinemathlearning.com/simil ... ngles.html
Awesome Nermal !!!

Got the same....actually since Midpoint theorem is not in the course of GMAT(nowhere OG talks about the same)...so I was hesitant to use the same directly and wanted to learn the approach that OG suggests.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times

by goelmohit2002 » Mon Sep 14, 2009 11:43 am
Thanks Guys for the discussion....OA = C.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 40
Joined: Sat Feb 14, 2009 9:22 am
GMAT Score:460

by GambitOS » Mon Sep 14, 2009 11:33 pm
:?:
Attachments
Triangle.jpg
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sun Jun 21, 2009 10:25 am
Location: Germany
Thanked: 7 times

by Nermal » Tue Sep 15, 2009 1:58 am
@GambitOS
Your point E is definitely not the midpoint of AC.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1799
Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members
Thanked: 36 times

by goelmohit2002 » Tue Sep 15, 2009 3:23 am
GambitOS wrote:Really? :)
Hi Gambit,

From Naked Eye I am not able to find out whether it is midpoint or not...can you please tell how to check the same in the figure that u drew ?

Any software that I can test ur figure ?

Thanks
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 40
Joined: Sat Feb 14, 2009 9:22 am
GMAT Score:460

by GambitOS » Tue Sep 15, 2009 3:27 am
:oops: Sorry guys, I recheck my figure. It's really parallel! :)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1