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

Redeem

What is the least common multiple of 39, 91, 93 and 217?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Elite Legendary Member
Posts: 3991
Joined: Fri Jul 24, 2015 2:28 am
Location: Las Vegas, USA
Thanked: 19 times
Followed by:37 members

What is the least common multiple of 39, 91, 93 and 217?

by Max@Math Revolution » Mon Feb 12, 2018 1:07 am
[GMAT math practice question]

What is the least common multiple of 39, 91, 93 and 217?

A. 8461
B. 8462
C. 8463
D. 8464
E. 8465
Top
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 555
Joined: Wed Oct 04, 2017 4:18 pm
Thanked: 180 times
Followed by:12 members

What is the least common multiple of 39, 91, 93 and 217?

by EconomistGMATTutor » Tue Feb 13, 2018 1:27 pm
GMAT math practice question]

What is the least common multiple of 39, 91, 93 and 217?

A. 8461
B. 8462
C. 8463
D. 8464
E. 8465
Hi Max@Math Revolution,
Let's take a look at your question.

To find the least common multiples of given numbers, we need to write the numbers a product of their prime factors.

39 = 3 x 13
91 = 7 x 13
93 = 3 x 31
217 = 7 x 31

Common Factors = 3, 13, 7, 31
Least Common Multiple = 3 x 13 x 7 x 31 = 8463

Therefore, Option C is correct.

Hope it helps. I am available if you'd like any follow up.
GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

Image
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8085
Joined: Sat Apr 25, 2015 10:56 am
Location: Los Angeles, CA
Thanked: 43 times
Followed by:29 members

by Scott@TargetTestPrep » Tue Feb 13, 2018 5:32 pm
Max@Math Revolution wrote:[GMAT math practice question]

What is the least common multiple of 39, 91, 93 and 217?

A. 8461
B. 8462
C. 8463
D. 8464
E. 8465
Prime factorizing each number, we have:

39 = 13 x 3

91 = 13 x 7

93 = 3 x 31

217 = 31 x 7

So the LCM is:

13 x 3 x 31 x 7

Rather than multiplying out the values, we can just calculate the units digit of our product by multiplying:

3 x 3 x 1 x 7 = 63, so the correct answer ends in a 3.

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
User avatar
Elite Legendary Member
Posts: 3991
Joined: Fri Jul 24, 2015 2:28 am
Location: Las Vegas, USA
Thanked: 19 times
Followed by:37 members

by Max@Math Revolution » Tue Feb 13, 2018 11:57 pm
=>

Since 39 = 3 * 13, the least common multiple must be a multiple of 3.
The sum of the digits of a multiple of 3 is a multiple of 3.
8643 is the only answer choice for which the sum of the digits is a multiple of 3: 8 + 4 + 6 + 3 = 21 = 3 * 7.

Therefore, C is the answer.

Alternatively, since 39 = 3*13, 91 = 7*13, 93 = 3*31, and 217=7*31, the least common multiple of the four numbers is 3*7*13*31 = 8463.

Therefore, the answer is C.

Answer: C
Top
Post new topic Post Reply
• Page 1 of 1