Which of the following are/is prime?

Expert replies

M7MBA: Moderator; Posts: 2058; Joined: Sun Oct 29, 2017 4:24 amFollowed by: 5 members; Thanked: 1 times

by M7MBA » Thu Mar 01, 2018 7:08 am

Which of the following are/is prime?

I. 143
II. 147
III. 149

(A) II only
(B) III only
(C) I & II
(D) I & III
(E) I, II, & III

The OA is the option B.

Experts, what is the faster way to solve this PS question? I know that 147 is not prime. But how can I determine if (I) or (III) are primes?

Like this post

Source: Beat The GMAT — Problem Solving | Thu Mar 01, 2018 7:08 am

GMAT/MBA Expert

Brent@GMATPrepNow: 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 » Thu Mar 01, 2018 7:13 am

M7MBA wrote:Which of the following are/is prime?

I. 143
II. 147
III. 149

(A) II only
(B) III only
(C) I & II
(D) I & III
(E) I, II, & III

I. 143
143 = 11 x 13
So, 143 is NOT prime.
ELIMINATE C, D and E

II. 147
Check the sum of the digits.
1+4+7 = 12
Since 12 is divisible by 3, we know that 147 is divisible by 3
So, 147 is NOT prime.
ELIMINATE A

By the process of elimination, the correct answer is B

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8137; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Fri Mar 02, 2018 9:56 am

M7MBA wrote:Which of the following are/is prime?

I. 143
II. 147
III. 149

(A) II only
(B) III only
(C) I & II
(D) I & III
(E) I, II, & III

Since 143 = 11 x 13, 143 is not a prime.

Since 147 = 7 x 21, 147 is not a prime.

149 is a prime since there is no multiplication of two numbers that equals 149 other than 1 x 149.

Answer: B

Scott Woodbury-Stewart
Founder and CEO
[email protected]

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

Like this post

BTGmoderatorRO: Moderator; Posts: 772; Joined: Wed Aug 30, 2017 6:29 pmFollowed by: 6 members

by BTGmoderatorRO » Fri Mar 02, 2018 12:02 pm

prime factors are numbers that are only divisible by one and its self.
Here,
i. 143 =11*13
ii. 147 =7*21
iii. 149=1*149
roman figure iii is an example of prime factors because it has only 2 factors which is 1 and 149.
Answer is b

Like this post

Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pmFollowed by: 5 members; Thanked: 6 times

by Vincen » Sat Mar 03, 2018 2:30 am

This is how I did it.

Since 147 is divisible by 3 (because 1+4+7=12 and it is divisible by 3) then I discarded the options (A), (C) and (E).

Now, watching the options (B) and (D) I knew that III is prime. Hence, I only had to check the option I = 143.

But 143=11*13, thus it is not prime.

Therefore, I concluded that B is the correct option.

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review