GMATPrep1
This topic has expert replies
- akhilsuhag
- Master | Next Rank: 500 Posts
- Posts: 351
- Joined: Mon Jul 04, 2011 10:25 pm
- Thanked: 57 times
- Followed by:4 members
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Hi akhilsuhag,
Looks like you posted this question twice: https://www.beatthegmat.com/gmatprep-2-t281566.html
Statement 1: m is a prime number
If m is a prime number, it has exactly 2 divisors (1 and m), so this tells us that the GCD of m and n must be either 1 or m.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT.
Statement 2: 2n = 7m
If 2n = 7m then we can rearrange the equation to get n = (7/2)m
IMPORTANT: Notice that if m were to equal an ODD number, then n would not be an integer. For example, if m = 3, then n = 21/2 (n is not an integer). Similarly, if m = 11, then n = 77/2 (n is not an integer). So, in order for n to be an INTEGER, m must be EVEN.
If m must be EVEN, there are several possible values for m and n. Consider these two cases:
case a: m = 2 and n = 7, in which case the GCD = 1
case b: m = 4 and n = 14, in which case the GCD=2
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT.
Statements 1 & 2 combined
From statement 1, we know that m is prime, and from statement 2, we know that m is even.
Since 2 is the only even prime number, we can conclude that m must equal 2.
If m = 2, then n must equal 7, which means that the GCD must be 1.
Since we are able to answer the target question with certainty, statements 1 & 2 combined are sufficient, and the answer is C
Cheers,
Brent
Looks like you posted this question twice: https://www.beatthegmat.com/gmatprep-2-t281566.html
Target question: What is the GCD of m and n?What is the greatest common divisor of positive integers m and n?
1) m is a prime number
2) 2n = 7m
Statement 1: m is a prime number
If m is a prime number, it has exactly 2 divisors (1 and m), so this tells us that the GCD of m and n must be either 1 or m.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT.
Statement 2: 2n = 7m
If 2n = 7m then we can rearrange the equation to get n = (7/2)m
IMPORTANT: Notice that if m were to equal an ODD number, then n would not be an integer. For example, if m = 3, then n = 21/2 (n is not an integer). Similarly, if m = 11, then n = 77/2 (n is not an integer). So, in order for n to be an INTEGER, m must be EVEN.
If m must be EVEN, there are several possible values for m and n. Consider these two cases:
case a: m = 2 and n = 7, in which case the GCD = 1
case b: m = 4 and n = 14, in which case the GCD=2
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT.
Statements 1 & 2 combined
From statement 1, we know that m is prime, and from statement 2, we know that m is even.
Since 2 is the only even prime number, we can conclude that m must equal 2.
If m = 2, then n must equal 7, which means that the GCD must be 1.
Since we are able to answer the target question with certainty, statements 1 & 2 combined are sufficient, and the answer is C
Cheers,
Brent
- akhilsuhag
- Master | Next Rank: 500 Posts
- Posts: 351
- Joined: Mon Jul 04, 2011 10:25 pm
- Thanked: 57 times
- Followed by:4 members
Hi Brent,
Thanks for your reply. Din post it twice, Mitch by mistake posted the reply to this is that post.
Regards.
Thanks for your reply. Din post it twice, Mitch by mistake posted the reply to this is that post.
Regards.
Please press "thanks" if you think my post has helped you.. Cheers!!
- akhilsuhag
- Master | Next Rank: 500 Posts
- Posts: 351
- Joined: Mon Jul 04, 2011 10:25 pm
- Thanked: 57 times
- Followed by:4 members
Hi Brent,
Thanks for your reply. Din post it twice, Mitch by mistake posted the reply to this is that post.
Regards.
Thanks for your reply. Din post it twice, Mitch by mistake posted the reply to this is that post.
Regards.
Please press "thanks" if you think my post has helped you.. Cheers!!
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
That's a funny turn of events!
You posted your response (about not posting twice) twice.
I think that happens if you press SUBMIT a second while the site is trying to download your first response.
You posted your response (about not posting twice) twice.
I think that happens if you press SUBMIT a second while the site is trying to download your first response.
- akhilsuhag
- Master | Next Rank: 500 Posts
- Posts: 351
- Joined: Mon Jul 04, 2011 10:25 pm
- Thanked: 57 times
- Followed by:4 members
Haha.. although could you help me with the other one. Still dont have an explanation (and have explanation for this one 3 times). People seem to really like explaining this one
Please press "thanks" if you think my post has helped you.. Cheers!!
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Too funny.akhilsuhag wrote:Haha.. although could you help me with the other one. Still dont have an explanation (and have explanation for this one 3 times). People seem to really like explaining this one
I saw Mitch's post (at https://www.beatthegmat.com/gmatprep-2-t ... tml#737782) and assumed it was the right question, and then posted my response.
I've edited my response to reflect the ACTUAL question.
Cheers,
Brent
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Fixed!akhilsuhag wrote:Mitch by mistake posted the reply to this is that post.
At https://www.beatthegmat.com/gmatprep-2-t ... tml#737782, you'll now find my solution for the problem actually posted there.
As for the problem posted above, here is my solution:
Statement 1 is clearly INSUFFICIENT.What is the greatest common divisor of positive integers m and n?
1) m is a prime number
2) 2n = 7m
When one of the statements is clearly insufficient, consider how it might affect the OTHER statement.
Since statement 1 is in terms of m, rephrase statement 2 in terms of m.
Statement 2: m = (2/7)n
The smallest possible value for n is 7.
Case 1: n=7, m = (2/7)(7) = 2.
The GCF of 2 and 7 is 1.
Case 2: n=14, m=(2/7)(14) = 4.
The GCF of 4 and 14 is 2.
Since the GCF can be different values, INSUFFICIENT.
Statements combined:
Cases 1 and 2 imply that m must be EVEN.
One more case to confirm:
Case 3: n=21, m = (2/7)(21) = 6.
Case 3 confirms that m must be even.
Since statement 1 indicates that m is prime, only Case 1 -- m=2, n=7 -- satisfies both statements.
In Case 1, the GCF m and n is 1.
SUFFICIENT.
The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3