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 →

greatest common divisor - confused????

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times
by Gurpinder » Tue Dec 15, 2009 9:21 am
hey guys,

i was reviewing for the gmat and was learning about the greatest common divisor stuff and came came across this question:

Which number is the greatest common divisor (GCD) of 45 and 75?
A. 3,375
B. 225
C. 15
D. 5
E. 3

my answer, after doing prime factorization was 15. the book says the answer is 225 :S:S:S howww?!?!?!?!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Fri Apr 24, 2009 1:13 am

by Hussain15 » Tue Dec 15, 2009 9:27 am
There must be a typo in the book, ur answer is correct.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times

by Gurpinder » Tue Dec 15, 2009 9:30 am
right????? thats what i have been thinkingg

because 225 is the LEAST COMMON MULTIPLE not the GC divisor.

hmmmm ok

thanks for ur reply!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Tue Nov 03, 2009 11:07 am

by tata » Wed Dec 16, 2009 12:19 pm
Gurpinder wrote:right????? thats what i have been thinkingg

because 225 is the LEAST COMMON MULTIPLE not the GC divisor.

hmmmm ok

thanks for ur reply!
No its the other way round, the LCM is 15 and the GCD is 225, OA is correct.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 15
Joined: Mon Nov 23, 2009 6:23 pm
Thanked: 1 times

by kabirmohammed » Wed Dec 16, 2009 1:18 pm
Multiples of 45: 45, 90, 135, 180, 225, 270,.......
Multiples of 75: 75, 150, 225, 300, .....
from the above multiples the Least common multiple(LCM) is 225

GCD of a,b = axb/(lcm(a,b)
= 45x75/225
=15
correct me if iam wrong..
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 17
Joined: Tue May 12, 2009 6:14 pm
Thanked: 1 times
GMAT Score:700

by nittanylion530 » Wed Dec 16, 2009 1:24 pm
Tata is correct. You are thinking about it backwards. LCM is 15 and GCD is 225.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 659
Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members
Thanked: 32 times

by Gurpinder » Wed Dec 16, 2009 1:44 pm
ummm noo....kabirmohamed is right.....gcd is 15.....lcm is 225
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 17
Joined: Tue May 12, 2009 6:14 pm
Thanked: 1 times
GMAT Score:700

by nittanylion530 » Wed Dec 16, 2009 2:25 pm
What's the source of this question?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members
Location: Montreal
Thanked: 1090 times
GMAT Score:780

by Ian Stewart » Wed Dec 16, 2009 4:37 pm
Some confusion in the posts above! The least common multiple of two numbers must be a multiple of both numbers; it will normally be larger than both numbers (occasionally it will be equal to the larger of the two). The LCM of 45 and 75 is 225.

The greatest common divisor of two numbers must be a divisor/factor of both numbers; it will normally be smaller than both numbers (occasionally it will be equal to the smaller of the two). The GCD of 45 and 75 is 15.

Any book that claims the GCD of 45 and 75 is 225 should probably be thrown in the bin! Which book is it, by the way?
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Senior | Next Rank: 100 Posts
Posts: 93
Joined: Mon Dec 14, 2009 4:15 am

by Lattefah84 » Thu Dec 17, 2009 12:19 am
Ian Stewart wrote:Some confusion in the posts above! The least common multiple of two numbers must be a multiple of both numbers; it will normally be larger than both numbers (occasionally it will be equal to the larger of the two). The LCM of 45 and 75 is 225.

The greatest common divisor of two numbers must be a divisor/factor of both numbers; it will normally be smaller than both numbers (occasionally it will be equal to the smaller of the two). The GCD of 45 and 75 is 15.

Any book that claims the GCD of 45 and 75 is 225 should probably be thrown in the bin! Which book is it, by the way?
I agree.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1