geometry tough questn

Expert replies

sukh: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Tue Nov 09, 2010 11:33 pm

by sukh » Tue Aug 23, 2011 8:10 am

ABCDEFGH is a cube. If the length of the diagonals DF, AG & CE are equal to sides of a triangle , then the circumradius of that triangle would be
a)equal to sides of the cube
b)under-root 3 times the sides of the cube
c) 1/ under-root 3 times the side of the cube
d) Indeterminate

Like this post

Source: Beat The GMAT — Quantitative Reasoning | Tue Aug 23, 2011 8:10 am

amit.phatak: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Fri Apr 22, 2011 10:51 pm

by amit.phatak » Tue Aug 23, 2011 12:20 pm

I think it is equal to side of the cube
Ans : A

Explanation :
lets say Side of the cube = a
diagonal = sqrt(3) * a
for equilateral triangle (with sides = DF, AG & CE) each side = sqrt(3) * a
circumradius of equilateral triangle = 2/3 * sqrt(3)/2 * side = 2/3 * sqrt(3)/2 * sqrt(3) * a

Therefore, circumradius = a = side of the cube.

Like this post

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed Aug 24, 2011 9:51 am

sukh wrote:ABCDEFGH is a cube. If the length of the diagonals DF, AG & CE are equal to sides of a triangle , then the circumradius of that triangle would be
a)equal to sides of the cube
b)under-root 3 times the sides of the cube
c) 1/ under-root 3 times the side of the cube
d) Indeterminate

Amit is correct - the answer is A.

Aside: I should point out that, on the GMAT, you are not required to know the definition of "circumradius."

The question is also somewhat confusing to follow, and the 4 answer choices indicate that it is not a true GMAT question.

I mention all of this so that students do not become overly concerned if they didn't get the correct answer.

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

Abhishek009: Master | Next Rank: 500 Posts; Posts: 359; Joined: Wed Mar 11, 2009 4:37 amFollowed by: 2 members; Location: Kolkata, India; Thanked: 50 times

by Abhishek009 » Sun Aug 28, 2011 9:56 am

sukh wrote:ABCDEFGH is a cube. If the length of the diagonals DF, AG & CE are equal to sides of a triangle , then the circumradius of that triangle would be
a)equal to sides of the cube
b)under-root 3 times the sides of the cube
c) 1/ under-root 3 times the side of the cube
d) Indeterminate

Length of the diagonals of a cube is : âˆš3 * a

Sides of the triangle are equal ( Derived from the following statement - diagonals DF, AG & CE are equal to sides of a triangle )

Now Sides of a triangle is âˆš3 * a

We know circumradius of an equilateral triangle is : (âˆš3/3)* sides of an equilateral triangle.

So circumradius of the triangle is :

(âˆš3/3) * âˆš3 * a => a

So option a follows !!

Abhishek

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review