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 →

What is the gcd of a, b, and c

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 1100
Joined: Sat May 10, 2014 11:34 pmFollowed by: 24 members
Location: New Delhi, India
Thanked: 205 times

by GMATinsight » Mon Jul 28, 2014 8:47 am
gmat_guy666 wrote:What is the gcd of a, b, and c

(1) gcd(a, b) = 3
(2) gcd(b, c) = 4

OAc
Question : GCD of (a, b, and c) = ?

Statement 1) GCD (a, b) = 3
Information about c is absent therefore
INSUFFICIENT

Statement 2) GCD (b, c) = 4
Information about a is absent therefore
INSUFFICIENT

Combining the Two statements
GCD (b, c) = 4 i.e. there is NO common factor between b and c except 4
i.e. if b = 4x then c = 4y where x and y DO NOT share any common factor other than 1

AND
GCD (a, b) = 3 i.e. there is NO common factor between a and b except 3
i.e. if a = 3z then b = 3w where z and w DO NOT share any common factor other than 1

i.e. b = multiple of 12
and a = odd multiple of 3
and c = multiple of 4 BUT NOT MULTIPLE OF 3

Therefore, GCD of (a,b,c) = 1
SUFFICIENT

Answer: Option C
"GMATinsight"Bhoopendra Singh & Sushma Jha
Most Comprehensive and Affordable Video Course 2000+ CONCEPT Videos and Video Solutions
Whatsapp/Mobile: +91-9999687183 l [email protected]
Contact for One-on-One FREE ONLINE DEMO Class Call/e-mail
Most Efficient and affordable One-On-One Private tutoring fee - US$40-50 per hour
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 1556
Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members
Thanked: 448 times
GMAT Score:650

by theCodeToGMAT » Mon Jul 28, 2014 8:48 am
To find GCD (A,B,C)

Statement 1:
GCD (A,B) = 3
A = 3 x _
B = 3 x _
We cannot deduce anything
INSUFFICIENT

Statement 2:
GCD (B,C) = 4
B = 4 x _
C = 4 x _
We cannot deduce anything
INSUFFICIENT

Combining...
A = 3 x _
B = 3 x 4 x _
C = 4 x _
GCD = 1
SUFFICIENT

{C}
R A H U L
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 1100
Joined: Sat May 10, 2014 11:34 pmFollowed by: 24 members
Location: New Delhi, India
Thanked: 205 times

by GMATinsight » Mon Jul 28, 2014 8:50 am
gmat_guy666 wrote:What is the gcd of a, b, and c

(1) gcd(a, b) = 3
(2) gcd(b, c) = 4

OAc
ALTERNATE METHOD :

Question : GCD of (a, b, and c) = ?

Statement 1) GCD (a, b) = 3
Information about c is absent therefore
INSUFFICIENT

Statement 2) GCD (b, c) = 4
Information about a is absent therefore
INSUFFICIENT

Combining the Two statements
If a = 3 then b = 12 (To satisfy statement 1 and 2 both) and c = 4

Therefore, GCD of (a,b,c) = 1
SUFFICIENT

Answer: Option C
"GMATinsight"Bhoopendra Singh & Sushma Jha
Most Comprehensive and Affordable Video Course 2000+ CONCEPT Videos and Video Solutions
Whatsapp/Mobile: +91-9999687183 l [email protected]
Contact for One-on-One FREE ONLINE DEMO Class Call/e-mail
Most Efficient and affordable One-On-One Private tutoring fee - US$40-50 per hour
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
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 » Mon Jul 28, 2014 2:59 pm
GMATinsight wrote:
Combining the Two statements
GCD (b, c) = 4 i.e. there is NO common factor between b and c except 4
i.e. if b = 4x then c = 4y where x and y DO NOT share any common factor other than 1
Since there's a risk of leading students astray with the above statement in green, I'd like to point out that, if the Greatest Common Divisor (GCD) of b and c is 4, then there are two other divisors (factors) that b and c could have in common. They could also share a common factor of 2 and, of course, share a common factor of 1.
For example, if b = 4 and c = 12, then b and c have 1, 2 and 4 as common factors (of which, 4 is the greatest)

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
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 » Mon Jul 28, 2014 3:10 pm
gmat_guy666 wrote:What is the gcd of a, b, and c

(1) gcd(a, b) = 3
(2) gcd(b, c) = 4
Just to be clear, the test-makers would never assume that test-takers are aware of the notation in this question. An official GMAT question would probably look more like this:
If a, b and c are positive integers, what is the greatest common divisor of a, b and c?

1) The greatest common divisor of a and b is 3
2) The greatest common divisor of b and c is 4
For this question, I'll apply the following concept: If N is the greatest common divisor of a and b, then a and b also have all factors of N in common.

Target question: What is the greatest common divisor of a, b and c?

Statement 1: The greatest common divisor of a and b is 3
No information about c, so statement 1 is NOT SUFFICIENT

Statement 2: The greatest common divisor of b and c is 4
No information about a, so statement 2 is NOT SUFFICIENT:

Statements 1 and 2 combined
Statement 1: Applying the green rule above, a and b have the following divisors in common: 1 and 3.
Statement 2: Applying the green rule above, b and c have the following divisors in common: 1, 2 and 4.
We're looking for a divisor in common with a, b AND c. The only factor they all share is 1.
So, the greatest common divisor of a, b and c is 1.
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1