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

Redeem

What is the LCM of the numbers 3, a, and 7, if ‘a’ is an

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Moderator
Posts: 7187
Joined: Thu Sep 07, 2017 4:43 pm
Followed by:23 members

What is the LCM of the numbers 3, a, and 7, if ‘a’ is an

by BTGmoderatorDC » Tue Jun 25, 2019 8:33 pm

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

What is the LCM of the numbers 3, a, and 7, if 'a' is an integer and a ≥ 3?

Statement 1. 'a' is a prime number greater than 2.
Statement 2. Both GCD (3, a) and LCM (3, a) are factors of the number 30.

OA E

Source: e-GMAT
Top
Source: — Data Sufficiency |

GMAT/MBA Expert

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

by Ian Stewart » Thu Jun 27, 2019 7:15 am

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

Statement 1 is not sufficient, because the LCM will be different if a=5 or if a=97.

For Statement 2, the GCD of 3 and anything must be a divisor of 3, so it could only be 1 or 3, and will always be a divisor of 30. So Statement 1 only tells us "the LCM of 3 and a is a divisor of 30". That will be true if a is 3 or 5 (among other possibilities), and we get a different answer to the original question using a=3 and a=5. Since 3 and 5 are both prime numbers, we've just used both Statements together, so the answer is E.
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
Post new topic Post Reply
• Page 1 of 1