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Re: If a,b, and c are prime numbers, do (a+b) and c have a common factor [#permalink]
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27 Jun 2016, 04:55
chetan2u wrote:
amitpaul527 wrote:
If a,b, and c are prime numbers, do \((a+b)\) and \(c\) have a common factor that is greater than 1?
(1) a,b, and c are all different prime numbers (2) \(c\neq{2}\)
Hi,
lets analyze the Q
1) If all three are same prime ans will be NO.. -- (3+3)=6 and 3-- factors 1 and 3
chetan2u, can you please explain why the answer is no when the primes are all the same. 3 is the common factor of 3 and 6, so the answer should be yes. What am I missing? Sorry if the question is confusing, my brain is fried right now.
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Re: If a,b, and c are prime numbers, do (a+b) and c have a common factor [#permalink]
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17 Jul 2016, 09:14
Each statement alone is not sufficient. Combined, two possibilities: If (a+b) = (2+3) and c is 5 (c must be different from 2) they will have a common factor of 5 If (a+b) = 11+7 and c is 5, they will NOT have a common factor.
For Yes/No DS questions, we need to have a definitive Yes or a definitive No. Combined - not sufficient. Answer E.
Re: If a,b, and c are prime numbers, do (a+b) and c have a common factor [#permalink]
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14 May 2017, 17:07
2
1
toby001 wrote:
Hi Banuel,
I got this question right, but I was wondering if statement 2 said that neither a, b, or c could be 2, that would be sufficient, right?
Thank you!
Nopes. The answer would still be E.
Let us modify the question =-->
If a,b, and c are prime numbers, do (a+b) and c have a common factor that is greater than 1? (1) a,b, and c are all different prime numbers (2) c≠2
Statment 1 --> 2,3,5 => YES 3,5,13 => NO
Hence not sufficient,
Statment 2 --> What if the primes are equal ? We need to consider the possibility when a=b=c Say z=b=c=7 So a+b=14 c=7 Clearly GCD≠1 Hence not sufficient.
Now combing the two statements => as a,c,b≠2 They are all odd primes. Still -> 3,5,7 => YES 3,5,11 => NO
Re: If a,b, and c are prime numbers, do (a+b) and c have a common factor [#permalink]
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15 May 2018, 03:02
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68% (00:45) correct 
