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Which of the following are/is prime?

This topic has 2 expert replies and 2 member replies

Which of the following are/is prime?

Post 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?

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Post 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

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Post 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

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Scott Woodbury-Stewart Founder and CEO

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GMAT/MBA Expert

Post 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

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Brent Hanneson – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

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Post 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.

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