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

Redeem

GMAT Exam pack 2 - DS - Geometry

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 97
Joined: Mon Aug 04, 2014 5:39 pm
Thanked: 1 times
Followed by:2 members

GMAT Exam pack 2 - DS - Geometry

by lucas211 » Thu Jun 23, 2016 3:55 am
Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
Attachments
Screen Shot 2016-06-23 at 13.49.00.png
Top
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 2663
Joined: Wed Jan 14, 2015 8:25 am
Location: Boston, MA
Thanked: 1153 times
Followed by:128 members
GMAT Score:770

by DavidG@VeritasPrep » Thu Jun 23, 2016 5:18 am
lucas211 wrote:Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
The ratio of the sides is 3:4:5, not the actual measurements. In other words, the actual measurements could be 3, 4, and 5 or they could be 6, 8, and 10, or 9, 12, 15, etc.
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Thu Jun 23, 2016 6:29 am
lucas211 wrote:Hello BTG

Would appreciate a little help on the question below, and especially why C is not the right answer.
My approach here is, that combined we know that the "3-4-5"-triangle is a right triangle (or is it ?).
Since we know that the diameter is AB (and therefore the longest line possible inscribed in the circle), we can determine the diameter to 5, and through this calculate the circumference.

Thanks in advance
David is absolutely right about the ratio v. length.

One thing I want to add: If statement 2 had told us that the lengths were 3, 4, and 5, we wouldn't actually have needed statement 1 as well. Any triangle that has side lengths in the ratio 3:4:5 must be a right triangle (just as any triangle with 3 equal sides must be equilateral). If we knew it was a right triangle, then we'd know that the hypotenuse must be the diameter of the circle.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Top
GMAT Instructor
Posts: 2630
Joined: Wed Sep 12, 2012 3:32 pm
Location: East Bay all the way
Thanked: 625 times
Followed by:119 members
GMAT Score:780

by Matt@VeritasPrep » Thu Jun 23, 2016 5:47 pm
If the ratio is 3:4:5, we could have 3:4:5, or 6:8:10, or 9:12:15, or ...

The devil is in the details!

As a general strategy tip, if a DS question seems to be an obvious C, run screaming from answer C!
Top
Post new topic Post Reply
• Page 1 of 1