Hello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
OA: D
Thanks,
Sri
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If n is an integer, is n positive?
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n is an integer.gmattesttaker2 wrote:Hello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
OA: D
Thanks,
Sri
1) (2n+1)/(n+1) is an integer
(n+(n+1))/(n+1) is an integer.
n/(n+1) + 1 is an integer.
Lets remove the +1 as integer +1 is integer.
Adding +1 and -1 to the numerator;
((n+1)-1)/(n+1) is an integer.
1-1/(n+1) is an integer.
therefore 1/(n+1) is an integer.
To satisfy this condition 1/1 is the only integer possible. Hence n=0. (not positive)
Hence Statement1 is SUFFICIENT.
2) n=-n
2n=0
n=0
(not positive)
Hence Statement2 is SUFFICIENT.
Choose D
There might be easier ways to solve this. This would have been my first approach on the test.
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Hi Sri,
This DS question is perfect for TESTing Values; it also has some Number Properties built into it.
We're told that N is an integer. We're asked if N is positive. This is a YES/NO question.
Fact 1: (2N+1)/(N+1) = an integer.
Let's TEST VALUES:
If N = 0, we have 1/1 = an integer and the answer to the question is NO (because 0 is a "null" value; it is NOT positive).
If N = -2, we have -3/-1 = 3 = an integer and the answer to the question is NO.
When attempting to test a positive integer, we run into a problem....there are NO positive integers that satisfy Fact 1. N cannot be 1,2,3,4,5,etc., so we have no valid test cases that are positive. Based on the information that we DO have, the answer is ALWAYS NO.
Fact 1 is SUFFICIENT
Fact 2: N = -N
In the realm of math, there's only one solution to this equal. N must = 0 and the answer to the question is NO.
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
This DS question is perfect for TESTing Values; it also has some Number Properties built into it.
We're told that N is an integer. We're asked if N is positive. This is a YES/NO question.
Fact 1: (2N+1)/(N+1) = an integer.
Let's TEST VALUES:
If N = 0, we have 1/1 = an integer and the answer to the question is NO (because 0 is a "null" value; it is NOT positive).
If N = -2, we have -3/-1 = 3 = an integer and the answer to the question is NO.
When attempting to test a positive integer, we run into a problem....there are NO positive integers that satisfy Fact 1. N cannot be 1,2,3,4,5,etc., so we have no valid test cases that are positive. Based on the information that we DO have, the answer is ALWAYS NO.
Fact 1 is SUFFICIENT
Fact 2: N = -N
In the realm of math, there's only one solution to this equal. N must = 0 and the answer to the question is NO.
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
Last edited by [email protected] on Wed Jun 07, 2017 6:23 pm, edited 1 time in total.
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Statement 1: (2n+1)/(n+1) is an integergmattesttaker2 wrote:Hello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
In other words, 2n+1 is a multiple of n+1.
If n>0, then the smallest possible multiple of n+1 -- after n+1 itself -- is as follows:
2(n+1) = 2n+2.
Thus, if n>0, it is not possible that 2n+1 -- a value LESS than 2n+2 -- is a multiple of n+1.
Implication:
n cannot be positive.
SUFFICIENT.
Statement 2: n=-n
Adding n to both sides, we get:
2n = 0
n = 0.
Thus, n is not positive.
SUFFICIENT.
The correct answer is D.
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But, my calculation says Statement 2 is not sufficient.[email protected] wrote:
Fact 2: N = -N
In the realm of math, there's only one solution to this equal. N must = 0 and the answer to the question is NO.
Fact 2 is SUFFICIENT
Final Answer: B
Statement 2:
n=-n
n+n=0
integer+integer=0
6+(-6)=0, (the summation of 2 integer will be zero if the integers are same value and carries opposite sign.
So, n=6,-6
---> not sufficient
adding the 2 statements:
The summation of 2 integer must be zero.
So, we can take these values as integer=6 and -6.
So, not sufficient.
Is there any mistake in my calculation?
thanks...
Statement 1:GMATGuruNY wrote:Statement 1: (2n+1)/(n+1) is an integergmattesttaker2 wrote:Hello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
In other words, 2n+1 is a multiple of n+1.
If n>0, then the smallest possible multiple of n+1 -- after n+1 itself -- is as follows:
2(n+1) = 2n+2.
Thus, if n>0, it is not possible that 2n+1 -- a value LESS than 2n+2 -- is a multiple of n+1.
Implication:
n cannot be positive.
SUFFICIENT.
Statement 2: n=-n
Adding n to both sides, we get:
2n = 0
n = 0.
Thus, n is not positive.
SUFFICIENT.
The correct answer is D.
(2n+1)/(n+1)=integer
(2n+1)=integer (n+1)
(2n+1)=integer+integer
2n+1=integer
2n=integer-1
2n=integer-----equation (1)
So, if n=6, then equation (1)becomes...
2*6=integer
12=integer, which is ok.
again, if n=-6, then equation (1) becomes..
2*(-6)=integer
-12=integer, which is ok.
So, n=6,-6
---> not sufficient
Statement 2:
n=-n
n+n=0
integer+integer=0
6+(-6)=0, (the summation of 2 integer will be zero if the integers are same value and carries opposite sign.
So, n=6,-6
---> not sufficient
adding the 2 statements:
The summation of 2 integer must be zero.
So, we can take these values as integer=6 and -6.
So, not sufficient.
So, E to me.
is there any mistake in my calculation?
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Hi iMyself,
To start, you can double-check your calculations by plugging the 'solutions' that you've calculated back into the 'source equation' to make sure that they're actually solutions. In Fact 1, neither 6 nor -6 actually fits... so that should tell you that something is off in your work. In Fact 2, the equation uses just one variable: N; however, you rewrote that equation as integer + integer = 0, implying that the two integers could be different numbers. That is NOT possible though - the equation should be...
N+N = 0
2N = 0
N = 0
So N MUST be 0 (it can't be anything else).
GMAT assassins aren't born, they're made,
Rich
To start, you can double-check your calculations by plugging the 'solutions' that you've calculated back into the 'source equation' to make sure that they're actually solutions. In Fact 1, neither 6 nor -6 actually fits... so that should tell you that something is off in your work. In Fact 2, the equation uses just one variable: N; however, you rewrote that equation as integer + integer = 0, implying that the two integers could be different numbers. That is NOT possible though - the equation should be...
N+N = 0
2N = 0
N = 0
So N MUST be 0 (it can't be anything else).
GMAT assassins aren't born, they're made,
Rich
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Jay@ManhattanReview
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'n is an integer' mean that n is one among {..., -3, -2, -1, 0, 1, 2, 3, ...}gmattesttaker2 wrote:Hello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
OA: D
Thanks,
Sri
we have to see whether n is one among {1, 2, 3, ...}.
S1: (2n+1)/(n+1) is an integer
(2n+1)/(n+1) = [n+(n+1)]/(n+1) = n/(n+1) + 1
"'n/(n+1) + 1' is an integer" mean that 'n/(n+1)' is an integer.
We see that if we take n as positive, the denominator is more than the numerator by 1, making n/(n+1) a fraction < 1. Thus n cannot be positive. The answer is NO. A unique answer. Sufficient.
S2: n = -n
'n = -n' mean that a number is equal to its negative; it is not possible with any number except 0. Thus, n = 0 (Non-positive). The answer is NO. A unique answer. Sufficient.
Answer: D
-Jay
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Another approach:
S1:
(2n + 1) / (n + 1) =>
(n + (n + 1)) / (n + 1) =>
n/(n + 1) + (n + 1)/(n + 1) =>
n/(n + 1) + 1
We're told that's an integer, so n/(n + 1) must be an integer. But this is only possible if n = 0. So we know the sole value of n, SUFFICIENT.
S2:
n = -n
Add n to both sides:
2n = 0
So again, n = 0, SUFFICIENT.
S1:
(2n + 1) / (n + 1) =>
(n + (n + 1)) / (n + 1) =>
n/(n + 1) + (n + 1)/(n + 1) =>
n/(n + 1) + 1
We're told that's an integer, so n/(n + 1) must be an integer. But this is only possible if n = 0. So we know the sole value of n, SUFFICIENT.
S2:
n = -n
Add n to both sides:
2n = 0
So again, n = 0, SUFFICIENT.
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There is a mistake: you're letting n assume two different values in the same equation. (You can't have n be 6 and -6 simultaneously.) I like the idea though!n=-n
n+n=0
integer+integer=0
6+(-6)=0, (the summation of 2 integer will be zero if the integers are same value and carries opposite sign.
So, n=6,-6
---> not sufficient
adding the 2 statements:
The summation of 2 integer must be zero.
So, we can take these values as integer=6 and -6.
So, not sufficient.
Is there any mistake in my calculation?
thanks...
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Rich - Request you to correct the hidden answer as both the statements individually are SUFFICIENT. Thank you for your response to the question.
[email protected] wrote:Hi Sri,
This DS question is perfect for TESTing Values; it also has some Number Properties built into it.
We're told that N is an integer. We're asked if N is positive. This is a YES/NO question.
Fact 1: (2N+1)/(N+1) = an integer.
Let's TEST VALUES:
If N = 0, we have 1/1 = an integer and the answer to the question is NO (because 0 is a "null" value; it is NOT positive).
If N = -2, we have -3/-1 = 3 = an integer and the answer to the question is NO.
When attempting to test a positive integer, we run into a problem....there are NO positive integers that satisfy Fact 1. N cannot be 1,2,3,4,5,etc., so we have no valid test cases that are positive. Based on the information that we DO have, the answer is ALWAYS NO.
Fact 1 is SUFFICIENT
Fact 2: N = -N
In the realm of math, there's only one solution to this equal. N must = 0 and the answer to the question is NO.
Fact 2 is SUFFICIENT
Final Answer: B
GMAT assassins aren't born, they're made,
Rich
Best Regards,
Rahul Sehgal
Rahul Sehgal
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Hi Rahul,
Nice catch. I've fixed the issue.
GMAT assassins aren't born, they're made,
Rich
Nice catch. I've fixed the issue.
GMAT assassins aren't born, they're made,
Rich
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Target question: Is n positive?gmattesttaker2 wrote: ↑Sun Jun 15, 2014 5:47 pmHello,
Can you please help with this:
If n is an integer, is n positive?
1) (2n+1)/(n+1) is an integer
2) n = -n
OA: D
Thanks,
Sri
Given: In is an integer
Statement 1:(2n+1)/(n+1) is an integer
Rewrite as: (n+1+n)/(n+1) is an integer
Rewrite as: (n+1)/(n+1) + n/(n+1) is an integer
Or... 1 + n/(n+1) is an integer
This means that n/(n+1) is an integer
How can this be? How can some number divided by a number that's 1 greater be an integer?
This ONLY WORKS if n = 0, so statement 1 is really telling us that n = 0
In other words, n is NOT positive
Since we can answer the target question with certainty, statement 1 is SUFFICIENT
Statement 2: n=-n
Add n to both sides to get: 2n = 0
Divide both sides by 2 to get: n = 0
So, n is NOT positive
Since we can answer the target question with certainty, statement 2 is SUFFICIENT
Answer = D
Cheers,
Brent
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