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M10-29

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M10-29 [#permalink]

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New post 16 Sep 2014, 00:43
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A
B
C
D
E

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  75% (hard)

Question Stats:

40% (00:44) correct 60% (00:46) wrong based on 131 sessions

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Re M10-29 [#permalink]

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New post 16 Sep 2014, 00:43
1
5
Official Solution:


(1) \(x + y\) is a prime number. Clearly insufficient, consider \(x=3\), \(y=2\) and \(x=5\), \(y=2\).

(2) Both \(x\) and \(y\) are less than 5. Also insufficient, consider \(x=3\), \(y=2\) and \(x=3\), \(y=3\). Note that on the GMAT, unless it is explicitly stated otherwise, different variables CAN represent the same number. So, \(x=y\) is a valid scenario.

(1)+(2) Either \(x=3\) and \(y=2\) or vice versa. In any case \(|x-y|=1\). Sufficient.


Answer: C
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Re M10-29 [#permalink]

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New post 15 Jan 2016, 07:12
I think this is a poor-quality question and I don't agree with the explanation. If C is correct then it satisfies stat 1 and sat2...Now, the only case possible is x=y=3 or 2...but x+y=4 or 6 is not a prime no
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Re: M10-29 [#permalink]

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New post 15 Jan 2016, 11:09
amritkumar05 wrote:
I think this is a poor-quality question and I don't agree with the explanation. If C is correct then it satisfies stat 1 and sat2...Now, the only case possible is x=y=3 or 2...but x+y=4 or 6 is not a prime no


Please read carefully: Either x=3 and y=2 or vice versa --> x + y = 5 = prime.
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Re: M10-29 [#permalink]

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New post 29 Jul 2016, 09:11
Wrong Solution: Please note if X=Y scenario is applicable the |x-y| will be zero, hence ambiguous as different values obtained in different cases.
Answer is E
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Re: M10-29 [#permalink]

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New post 29 Jul 2016, 09:12
sorry got it x+y=5....got it
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Re: M10-29 [#permalink]

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New post 02 Apr 2017, 21:43
what if x & y are negative?
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Re: M10-29 [#permalink]

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New post 02 Apr 2017, 21:50
Hobbit20 wrote:
what if x & y are negative?


x and y cannot be negative because it's given in the stem that they are primes and only positive integers can be primes.

Check for more here: https://gmatclub.com/forum/math-number- ... 88376.html

Hope it helps.
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Re: M10-29 [#permalink]

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New post 04 Apr 2017, 10:17
Hi Bunuel,

When I was taking test I thought 2 is enough by itself because I thought x=3 and y=2 or vice versa.I guess I forgot about both number might be same. I mean 3-3 or 2-2, right?
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Re: M10-29 [#permalink]

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Re: M10-29 [#permalink]

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New post 10 Jun 2017, 00:55
Very good question. I forgot to include two pairs (2,2) and (3,3) for B.
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Re M10-29 [#permalink]

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New post 21 Jun 2017, 06:35
I think this is a high-quality question and I agree with explanation.
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Re: M10-29 [#permalink]

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New post 27 Aug 2017, 10:45
Bunuel wrote:
Hobbit20 wrote:
what if x & y are negative?


x and y cannot be negative because it's given in the stem that they are primes and only positive integers can be primes.

Check for more here: https://gmatclub.com/forum/math-number- ... 88376.html

Hope it helps.


Why prime numbers need to be always positive?
-2,-3,-5 also have 1 and the number itself as factor.
Then why can't we consider them prime?
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Re: M10-29 [#permalink]

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New post 27 Aug 2017, 11:01
buan15 wrote:
Bunuel wrote:
Hobbit20 wrote:
what if x & y are negative?


x and y cannot be negative because it's given in the stem that they are primes and only positive integers can be primes.

Check for more here: https://gmatclub.com/forum/math-number- ... 88376.html

Hope it helps.


Why prime numbers need to be always positive?
-2,-3,-5 also have 1 and the number itself as factor.
Then why can't we consider them prime?


By definition a prime number is a positive integer that has no positive integer divisors other than 1 and itself.

So just remember it and don't worry about it.

(The main reason we have this restrictions in definition is that if we remove them there will be some problems with fundamental theorem of arithmetic (unique prime factorization theorem), so removing them would require many other adjustment).
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

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Re M10-29 [#permalink]

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New post 17 Jun 2018, 12:30
I think this is a high-quality question and I agree with explanation.
Re M10-29   [#permalink] 17 Jun 2018, 12:30
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