Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Radius of Circle

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 156
Joined: Sun Jul 15, 2012 12:03 pmFollowed by: 1 member
Location: New York, USA
Thanked: 34 times
by kartikshah » Fri Jul 27, 2012 6:11 pm
What is the radius of the circle that circumscribes the triangle, measure of whose sides is 9, 40 and 41?

A. 20

B. 20.5

C. 4

D. 8

E. 45
Top
Join the discussion
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 342
Joined: Wed Jul 08, 2009 8:50 amFollowed by: 19 members
Thanked: 214 times
GMAT Score:740

by Birottam Dutta » Fri Jul 27, 2012 6:22 pm
The triangle specified here is a right angled triangle (9^2 + 40^2 = 41^2).

Always remember that in a right triangle, the hypotenuse is the diameter of the circumcircle and the centre is exactly the mid point of the hypotenuse.

So, diameter here is 41 and so, radius = 41/2 = 20.5

Answer B!
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 130
Joined: Fri Apr 20, 2012 8:13 amFollowed by: 4 members
Location: Toronto, Ontario
Thanked: 16 times
GMAT Score:650

by tisrar02 » Fri Jul 27, 2012 6:35 pm
Birottam Dutta wrote:The triangle specified here is a right angled triangle (9^2 + 40^2 = 41^2).

Always remember that in a right triangle, the hypotenuse is the diameter of the circumcircle and the centre is exactly the mid point of the hypotenuse.

So, diameter here is 41 and so, radius = 41/2 = 20.5

Answer B!

Quick question but how did you know right off the bat, that this triangle HAD to be a right triangle?
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 126
Joined: Sun Jun 24, 2012 10:11 amFollowed by: 7 members
Location: Chicago, IL
Thanked: 36 times

by tutorphd » Fri Jul 27, 2012 7:36 pm
The general problem of this type requires quite a messy trigonometry. GMAT problems never require trigonometry. Instead, they exploit special simplified cases that are solvable with simpler methods.

If the problem seems too complicated in general, always check for a special case: whether the triangle is right (Pythagorean triplets, 30-60-90, 45-45-90), isosceles, or equilateral.
Skype / Chicago quant tutor in GMAT / GRE
https://gmat.tutorchicago.org/
Top
Join the discussion