Sorry to ask this once again. But still trying to understand why B is the correct answer.
If a=b=1 and n=0 then the second option becomes 1+1 which is divisible by a+b(2).
Doesn't this mean we get both ZERO and all ODD values not satisfying the second option. Hence unable to answer the question: is n odd?
Can someone clarify.
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DS + nth power
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rohan.saha86
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for a^n-b^n, you can pick n=2 or 3 and it is divisible in either case so 1) is not sufficient
For a^n+b^n, again piking the values n=2 or 3, we can see that for n=2 it is definitiely not divisible by a+b
Hence, 2.) is sufficient, and answer is B)
For a^n+b^n, again piking the values n=2 or 3, we can see that for n=2 it is definitiely not divisible by a+b
Hence, 2.) is sufficient, and answer is B)
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krusta80
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(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
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fangtray
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ian gave an example where a^n +b^n is divisible by a+b. for example, n=2 a=20 b=5. what am i missing here? how come its still b?>krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
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fangtray
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ian gave an example where a^n +b^n is divisible by a+b. for example, n=2 a=20 b=5. what am i missing here? how come its still b?>krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
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fangtray
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ian gave an example where a^n +b^n is divisible by a+b. for example, n=2 a=20 b=5. what am i missing here? how come its still b?>krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
Folks,
I have 3 comments to the posted question:
1) the answer is definitely not A, B, or D. In fact, i think the answer is E.
2) i don't think you can apply any general rule without specifying restrictions on the values of a, b, and n. The answer highly depends on the values of a, b, and n. If you consider various possibilities for these variables (e.g., a=b, a =odd and b=even, one of them negative and another positive, n being negative), you will find that the answer is not concrete (can be yes or no)
3) for a question such as this one, i would simply guess and move on. It is not worth spending the time during the test to examine various scenarios even though it may be highly tempting to get the right answer. Any extra time you spend to solve such a question is less time for other questions and the chances of getting penalized for not completing the section increases. GMAT is not about only being right, but also being smart. Be strategic.
I have 3 comments to the posted question:
1) the answer is definitely not A, B, or D. In fact, i think the answer is E.
2) i don't think you can apply any general rule without specifying restrictions on the values of a, b, and n. The answer highly depends on the values of a, b, and n. If you consider various possibilities for these variables (e.g., a=b, a =odd and b=even, one of them negative and another positive, n being negative), you will find that the answer is not concrete (can be yes or no)
3) for a question such as this one, i would simply guess and move on. It is not worth spending the time during the test to examine various scenarios even though it may be highly tempting to get the right answer. Any extra time you spend to solve such a question is less time for other questions and the chances of getting penalized for not completing the section increases. GMAT is not about only being right, but also being smart. Be strategic.
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krusta80
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fangtray wrote:Can someone verify whether the original question places a non-negative restriction on n?krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
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sanju09
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krusta80 wrote:The original question should have placed the non-negativity constraint for n, otherwise this would prove to be fairly unGMATtish! (new term)fangtray wrote:Can someone verify whether the original question places a non-negative restriction on n?krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
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Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
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sanju09
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a^n + b^n is divisible by a + b only when n is an odd positive integer, and a and/or b are non zero numbers. You cannot take n = 2 to prove this point, fangtray.fangtray wrote:ian gave an example where a^n +b^n is divisible by a+b. for example, n=2 a=20 b=5. what am i missing here? how come its still b?>krusta80 wrote:(1) a^n - b^n is divisible by a - bharsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
This works for n = 1 -> a-b mod a-b = 0
This also works for any even n >= 2 -> a^2-b^2 -> (a-b)(a+b) mod (a-b) = 0
INSUFF
(2) a^n + b^n is NOT divisible by a+b
SUFF
B
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
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Ganesh hatwar
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E bcoz i am not getting !!harsh.champ wrote:Is n odd ?
1. a^n - b^n is divisible by a - b
2. a^n + b^n is not divisible by a + b
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surmilsehgal
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rahul.neemuch
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Hi guys
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
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rahul.neemuch
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Hi guys
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
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rahul.neemuch
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Hi guys
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
Pls reply to my query.
Why nt the ans is E.
a n b are real nos. If we take a=3/2, b=1/2 then even if n is odd a^n+b^n is not divisible by a+b.
