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This topic is locked. If you want to discuss this question please repost it in the respective forum. \(X\) and \(Y\) are prime integers. What is \(X + Y\) ? 1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\) Source: GMAT Club Tests  hardest GMAT questions Is 1 considered a prime number? I selected C but was wrong. According to the answer: S2 is not sufficient. Consider \(X = 5\) , \(Y = 3\) and \(X = 3\) , \(Y = 2\) which is true... edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?



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Re: Prime Numbers [#permalink]
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sharmar wrote: \(X\) and \(Y\) are prime integers. What is \(X + Y\) ?
1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\)
(C) 2008 GMAT Club  m25#29
* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient * Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient * BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient * EACH statement ALONE is sufficient * Statements (1) and (2) TOGETHER are NOT sufficient
Is 1 considered a prime number? I selected C but was wrong. According to the answer: S2 is not sufficient. Consider \(X = 5\) , \(Y = 3\) and \(X = 3\) , \(Y = 2\) which is true...
edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something? 1) X  Y is prime case 1: 5  2 = 3 5 + 2 = 7 case 2: 7  5 = 2 7 + 5 = 13 Two answers. Insufficient. 2) Y < X < 6 Possible value for Y = {2, 3} Possible value for X = {3, 5} More than one answer. Insufficient. 1) & 2) Case 1: 2 < 3 < 6 3  2 = 1  Not Prime Drop this case Case 2: 2 < 5 < 6 5  2 = 3  Prime 5 + 2 = 7 Case 3: 3 < 5 < 6 5  3 = 2  Prime 5 + 3 = 8 Two answers, Insufficient. The answer is E.



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Re: Prime Numbers [#permalink]
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[quote="sharmar"]\(X\) and \(Y\) are prime integers. What is \(X + Y\) ?
1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\)
the difference between consecutive primes = /2/ except 2,3 = /1/
from 1
x,y could be any prime >3....insuff
from 2
obviously not suff
both
no idea if they are consec or not ...insuff
E is my answer



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Re: Prime Numbers [#permalink]
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sharmar wrote: Nevermind... I think I figured it out... I didn't consider 52 = 3 ALSO CONSIDER 72 = 5 OR 75 = 2 SOME MORE 13  2 = 11 AND 13  2 = 11
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Re: M25 #29 [#permalink]
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02 Jul 2010, 05:19
isnt 1 a prime number ?



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Re: M25 #29 [#permalink]
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02 Jul 2010, 06:05
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No, 1 is not considered a prime. A prime number (or a prime) is a natural number that has exactly two distinct natural number divisors: 1 and itself.
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Re: M25 #29 [#permalink]
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05 Jul 2010, 20:53
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X and Y are prime integers. What is X+Y ?
1. XY is a prime integer 2. Y<X<6
Case 1: XY is prime number Set (X,Y) : (5,2), (5,3),(7,2),(7,5),(13,2)(13,11). No Unique Soln.
Case 2. Y<X<6 Set (X,Y) : (5,3),(5,2)(3,2) No Unique Soln.
Combining Case 1 & Case 2 : no Unique Soln.
Thus E: Stmt 1 & Stmt 2 Together are not sufficient.



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Re: M25 #29 [#permalink]
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06 Jul 2011, 14:38
1 simple question : are negative prime numbers considered in GMAT ? If yes, this question can be solved in 30 sec....else the 3,2 explanation is correct
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Re: M25 #29 [#permalink]
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14 Jul 2011, 08:30
Prime number is an integer number P\(>=\)2, divisible by only itself and 1.
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Re: M25 #29 [#permalink]
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30 Jul 2011, 00:44
Some folks here say 1 is not a prime. But it is.
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Re: M25 #29 [#permalink]
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27 Mar 2012, 02:09
sharmar wrote: \(X\) and \(Y\) are prime integers. What is \(X + Y\) ? 1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\) Source: GMAT Club Tests  hardest GMAT questions Is 1 considered a prime number? I selected C but was wrong. According to the answer: S2 is not sufficient. Consider \(X = 5\) , \(Y = 3\) and \(X = 3\) , \(Y = 2\) which is true... edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something? If \(x\) and \(y\) are prime numbers, what is the value of \(x+y\) ? (1) \(xy\) is a prime number > if \(x=5\) and \(y=2\) (notice that in this case \(xy=3=prime\)) then \(x+y=7\) but if \(x=5\) and \(y=3\) (notice that in this case \(xy=2=prime\)) then \(x+y=8\). Not sufficient. (2) \(y<x<6\) > the same example as above is valid for this statement also. Not sufficient. (1)+(2) Again, the example from statement (1) is still valid and gives two different values for \(x+y\). Not sufficient. Answer: E.
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Re: M25 #29 [#permalink]
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27 Mar 2012, 04:18



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Re: M25 #29 [#permalink]
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11 Jul 2012, 23:17
Question can be answered by using both the statements together x=5 y=3 xy=2 which is a prime number and yes 1 is not prime..



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Re: M25 #29 [#permalink]
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31 Aug 2012, 21:08
Good question. I am particularly happy that I did end up solving this one is about a min and half. Followed the plugging in of values approach with values as 5,2,3 for statement (ii) and for statement (i) there are a whole number of possible options. Both statements together as well fail to give a concrete answer for the values 2,3,5. Hence chose E.
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18 Sep 2012, 06:16
Picking up on bunnels statement re: 1 being a prime.... If you have trouble remembering in the heat of battle, think: a prime number has 2 factors, 1 and itself. Although 1 has factors of 1 and iteslf, these are one and the same and therefore it doesn't have 2 (intiger) factors.
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Re: M25 #29 [#permalink]
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10 Jul 2013, 05:11
Bunuel wrote: sharmar wrote: \(X\) and \(Y\) are prime integers. What is \(X + Y\) ? 1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\) Source: GMAT Club Tests  hardest GMAT questions Is 1 considered a prime number? I selected C but was wrong. According to the answer: S2 is not sufficient. Consider \(X = 5\) , \(Y = 3\) and \(X = 3\) , \(Y = 2\) which is true... edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something? If \(x\) and \(y\) are prime numbers, what is the value of \(x+y\) ? (1) \(xy\) is a prime number > if \(x=5\) and \(y=2\) (notice that in this case \(xy=3=prime\)) then \(x+y=7\) but if \(x=5\) and \(y=3\) (notice that in this case \(xy=2=prime\)) then \(x+y=8\). Not sufficient. (2) \(y<x<6\) > the same example as above is valid for this statement also. Not sufficient. (1)+(2) Again, the example from statement (1) is still valid and gives two different values for \(x+y\). Not sufficient. Answer: E. Can we also consider negative cases of these integers, since the question did not explicitly state that the integers were positive?
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Re: M25 #29 [#permalink]
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10 Jul 2013, 06:13
knightofdelta wrote: Bunuel wrote: sharmar wrote: \(X\) and \(Y\) are prime integers. What is \(X + Y\) ? 1. \(X  Y\) is a prime integer 2. \(Y \lt X \lt 6\) Source: GMAT Club Tests  hardest GMAT questions Is 1 considered a prime number? I selected C but was wrong. According to the answer: S2 is not sufficient. Consider \(X = 5\) , \(Y = 3\) and \(X = 3\) , \(Y = 2\) which is true... edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something? If \(x\) and \(y\) are prime numbers, what is the value of \(x+y\) ? (1) \(xy\) is a prime number > if \(x=5\) and \(y=2\) (notice that in this case \(xy=3=prime\)) then \(x+y=7\) but if \(x=5\) and \(y=3\) (notice that in this case \(xy=2=prime\)) then \(x+y=8\). Not sufficient. (2) \(y<x<6\) > the same example as above is valid for this statement also. Not sufficient. (1)+(2) Again, the example from statement (1) is still valid and gives two different values for \(x+y\). Not sufficient. Answer: E. Can we also consider negative cases of these integers, since the question did not explicitly state that the integers were positive? No, we cannot. "If \(x\) and \(y\) are prime numbers..." Only positive numbers can be primes. Hope it helps.
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Re: M25 #29 [#permalink]
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10 Jul 2013, 07:25
petrifiedbutstanding wrote: Some folks here say 1 is not a prime. But it is. Natural numbers that have EXACTLY two factors are called prime numbers. Obviously, the number "1" has exactly 1 factor, so it is neither prime nor composite.. Yeah, this number is a different breed !!
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10 Jul 2013, 07:27
heartbeats1987 wrote: petrifiedbutstanding wrote: Some folks here say 1 is not a prime. But it is. Natural numbers that have EXACTLY two factors are called prime numbers. Obviously, the number "1" has exactly 1 factor, so it is neither prime nor composite.. Yeah, this number is a different breed !! Right. So if I see "different breed" on a GMAT DS, I should think "1" right?
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