Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized for You
we will pick new questions that match your level based on your Timer History
Track Your Progress
every week, we’ll send you an estimated GMAT score based on your performance
Practice Pays
we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
It appears that you are browsing the GMAT Club forum unregistered!
Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club
Registration gives you:
Tests
Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.
Applicant Stats
View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more
Books/Downloads
Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Is N divisible by 7? [#permalink]
07 Feb 2012, 14:12
3
This post was BOOKMARKED
00:00
A
B
C
D
E
Difficulty:
5% (low)
Question Stats:
73% (01:40) correct
27% (00:37) wrong based on 163 sessions
Is N divisible by 7?
(1) N = x-y, where x and y are integers (2) x is divisible by 7, and y is not divisible by 7
Hi guys, my question is not in regards to how to solve this problem, but how to know if the answer is required to be an integer or not? For example, the question above does not mention any requirements for the answer to be an integer, yet that is exactly what the outcome requires. Any help would be greatly appreciated.
Re: Is N divisible by 7? [#permalink]
07 Feb 2012, 14:22
2
This post received KUDOS
Expert's post
Aple wrote:
Is N divisible by 7?
(1) N = x-y, where x and y are integers (2) x is divisible by 7, and y is not divisible by 7
Hi guys, my question is not in regards to how to solve this problem, but how to know if the answer is required to be an integer or not? For example, the question above does not mention any requirements for the answer to be an integer, yet that is exactly what the outcome requires. Any help would be greatly appreciated.
Thanks
N to be divisible by 7, it MUST be an integer (at least on the GMAT) because the question makes no sense if N is not an integer. On the GMAT divisibility is applied only to the integers.
Also on GMAT when we are told that \(a\) is divisible by \(b\) (or which is the same: "\(a\) is multiple of \(b\)", or "\(b\) is a factor of \(a\)"), we can say that: 1. \(a\) is an integer; 2. \(b\) is an integer; 3. \(\frac{a}{b}=integer\).
As for the question: Is N divisible by 7?
(1) N = x-y, where x and y are integers. Clearly insufficient. (2) x is divisible by 7, and y is not divisible by 7. Clearly insufficient.
(1)+(2) N={multiple of 7}-{not a multiple of 7}={not a multiple of 7}. Sufficient.
Answer: C.
Below might help to understand this concept better.
If integers \(a\) and \(b\) are both multiples of some integer \(k>1\) (divisible by \(k\)), then their sum and difference will also be a multiple of \(k\) (divisible by \(k\)): Example: \(a=6\) and \(b=9\), both divisible by 3 ---> \(a+b=15\) and \(a-b=-3\), again both divisible by 3.
If out of integers \(a\) and \(b\) one is a multiple of some integer \(k>1\) and another is not, then their sum and difference will NOT be a multiple of \(k\) (divisible by \(k\)): Example: \(a=6\), divisible by 3 and \(b=5\), not divisible by 3 ---> \(a+b=11\) and \(a-b=1\), neither is divisible by 3.
If integers \(a\) and \(b\) both are NOT multiples of some integer \(k>1\) (divisible by \(k\)), then their sum and difference may or may not be a multiple of \(k\) (divisible by \(k\)): Example: \(a=5\) and \(b=4\), neither is divisible by 3 ---> \(a+b=9\), is divisible by 3 and \(a-b=1\), is not divisible by 3; OR: \(a=6\) and \(b=3\), neither is divisible by 5 ---> \(a+b=9\) and \(a-b=3\), neither is divisible by 5; OR: \(a=2\) and \(b=2\), neither is divisible by 4 ---> \(a+b=4\) and \(a-b=0\), both are divisible by 4.
Re: Is N divisible by 7? [#permalink]
07 Feb 2012, 14:30
2
This post received KUDOS
Expert's post
Aple wrote:
Is N divisible by 7?
(1) N = x-y, where x and y are integers (2) x is divisible by 7, and y is not divisible by 7
Hi guys, my question is not in regards to how to solve this problem, but how to know if the answer is required to be an integer or not? For example, the question above does not mention any requirements for the answer to be an integer, yet that is exactly what the outcome requires. Any help would be greatly appreciated.
Thanks
One more thing: every GMAT divisibility question will tell you in advance that any unknowns represent positive integers.
So, if it were realistic GMAT question it would most probably ask: If N is an integer, is N divisible by 7? _________________
Re: Is N divisible by 7? [#permalink]
07 Feb 2012, 15:33
Thank you for all the information, it was very helpful, I was just unclear previously because when I read the question "Is N divisible by 7" I looked at it as: 1/7 is possible, but will be a decimal. With no other information stating it is required to be an integer I felt it was an acceptable answer. I was just unsure if I had missed some information or have not been looking at the question appropriately.
Re: Is N divisible by 7? [#permalink]
20 May 2012, 17:27
Statement 1: N = x-y where x and y are integers. Clearly, the difference of two integers can be any other integer, and some integers are divisible by 7 while others are not. Insufficient.
Statement 2: x and y are not defined. Insufficient.
Combining both statements, N = x - y where x is divisible by 7 and y is not divisible by 7 = multiple of 7 - (non multiple of 7) = not divisible by 7 Sufficient.
Re: Is N divisible by 7? [#permalink]
14 May 2015, 05:56
Hello from the GMAT Club BumpBot!
Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________
Re: Is N divisible by 7? [#permalink]
19 May 2015, 22:17
If any 2 integers are divisible by a number , then sum and subtraction of the integers should also be divisible by the number . For Ex:- if x and y both are factors of 2, then x-y and x+y will also be factors of 2 .
Re: Is N divisible by 7? [#permalink]
19 May 2015, 22:23
Expert's post
ss142012 wrote:
If any 2 integers are divisible by a number , then sum and subtraction of the integers should also be divisible by the number . For Ex:- if x and y both are factors of 2, then x-y and x+y will also be factors of 2 .
Experts please reply .
Yes, say the common factor is x.
So the numbers are ax and bx.
Sum = ax + bx = x (a + b) => divisible by x Difference = ax - bx = x(a - b) => divisible by x (assuming a > b. If b is greater, then difference will be bx - ax)
The “3 golden nuggets” of MBA admission process With ten years of experience helping prospective students with MBA admissions and career progression, I will be writing this blog through...
You know what’s worse than getting a ding at one of your dreams schools . Yes its getting that horrid wait-listed email . This limbo is frustrating as hell . Somewhere...