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Can the positive integer n be written as the sum of two

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Can the positive integer n be written as the sum of two [#permalink] New post 29 Jan 2012, 10:56
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Can the positive integer n be written as the sum of two different positive prime numbers?

(1) n is greater than 3.
(2) n is odd.

When I am checking the case using both conditions so can i rephrase problem statement as "Can every odd integer which is greater than 3 can be written as sum of two positive integers " OR
"Can any odd integer which is greater than 3 can be written as sum of two positive integers"
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Re: Rephrasing [#permalink] New post 29 Jan 2012, 11:40
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monikaleoster wrote:
90. Can the positive integer n be written as the sum of two different positive prime numbers?
(1) n is greater than 3.
(2) n is odd.

When I am checking the case using both conditions so can i rephrase problem statement as "Can every odd integer which is greater than 3 can be written as sum of two positive integers " OR
"Can any odd integer which is greater than 3 can be written as sum of two positive integers"


Note that n is some particular, fixed number. If we take two statements together the question becomes: can odd integer n, which is greater than 3, be written as the sum of two different prime numbers?

Now, if EVERY odd integer greater than 3 can be written as the sum of two different prime numbers, then taken together statements would be sufficient as we get definite YES answer to the question (because if it can be done for EVERY odd integer greater than 3 then it can be done for some particular n, from this group, too). Also, if NEITHER odd integer greater than 3 can be written as the sum of two different prime numbers, then taken together statements would still be sufficient, though at this time we'd get definite NO answer to the question (because if it cannot be done for ANY odd integer greater than 3 then it can not be done for some particular n, from this group, too).

Next, if we can find two values of odd integer n greater than 3 and one of them can be written as the sum of two different prime numbers and another cannot, then taken together statements would NOT be sufficient.

For this question the answer is E:
If n=5=odd>3, then the answer would be YES, 5=2+3=prime+prime;
If n=11=odd>3, then the answer would be NO, (11=odd and in order it to be the sum of two different primes one must be 2=even=prime, in this case another number would be 9, since 9 is not a prime, you cannot write 11 as the sum of two different primes).

So, we have two values of odd integer n greater than 3: one of them can be written as the sum of two different prime numbers and another cannot, hence taken together statements are not sufficient.

Answer: E.

Hope it's clear.
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Re: Can the positive integer n be written as the sum of two [#permalink] New post 30 Jan 2012, 09:55
Thanks for wonderful Explanation..:)
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Re: Rephrasing [#permalink] New post 14 Mar 2013, 17:24
Bunuel wrote:
monikaleoster wrote:
90. Can the positive integer n be written as the sum of two different positive prime numbers?
(1) n is greater than 3.
(2) n is odd.

When I am checking the case using both conditions so can i rephrase problem statement as "Can every odd integer which is greater than 3 can be written as sum of two positive integers " OR
"Can any odd integer which is greater than 3 can be written as sum of two positive integers"


Note that n is some particular, fixed number. If we take two statements together the question becomes: can odd integer n, which is greater than 3, be written as the sum of two different prime numbers?

Now, if EVERY odd integer greater than 3 can be written as the sum of two different prime numbers, then taken together statements would be sufficient as we get definite YES answer to the question (because if it can be done for EVERY odd integer greater than 3 then it can be done for some particular n, from this group, too). Also, if NEITHER odd integer greater than 3 can be written as the sum of two different prime numbers, then taken together statements would still be sufficient, though at this time we'd get definite NO answer to the question (because if it cannot be done for ANY odd integer greater than 3 then it can not be done for some particular n, from this group, too).

Next, if we can find two values of odd integer n greater than 3 and one of them can be written as the sum of two different prime numbers and another cannot, then taken together statements would NOT be sufficient.

For this question the answer is E:
If n=5=odd>3, then the answer would be YES, 5=2+3=prime+prime;
If n=11=odd>3, then the answer would be NO, (11=odd and in order it to be the sum of two different primes one must be 2=even=prime, in this case another number would be 9, since 9 is not a prime, you cannot write 11 as the sum of two different primes).

So, we have two values of odd integer n greater than 3: one of them can be written as the sum of two different prime numbers and another cannot, hence taken together statements are not sufficient.

Answer: E.

Hope it's clear.


solved it correctly but could not find a clear takeaway for this problem
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Re: Can the positive integer n be written as the sum of two [#permalink] New post 14 Mar 2013, 21:50
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monikaleoster wrote:
Can the positive integer n be written as the sum of two different positive prime numbers?

(1) n is greater than 3.
(2) n is odd.



Nothing new to add after Bunuel's explanation. But just to point down what I observed for F.S 2;we know that n is odd. Again we have been asked if n is a sum of 2 different primes. Now we know that only odd+even = odd. Thus out of the two given prime numbers, we can have only 2 as the even prime. So now the statement basically states that if we subtract 2 from n, do we end up with a prime greater than 2.

or Is n-2 = a prime greater than 2. Take any odd integer for n. For n=13, we get a YES. For n=17, we get a NO. Insufficient.
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Re: Can the positive integer n be written as the sum of two [#permalink] New post 16 Mar 2013, 13:08
vinaymimani wrote:
monikaleoster wrote:
Can the positive integer n be written as the sum of two different positive prime numbers?

(1) n is greater than 3.
(2) n is odd.



Nothing new to add after Bunuel's explanation. But just to point down what I observed for F.S 2;we know that n is odd. Again we have been asked if n is a sum of 2 different primes. Now we know that only odd+even = odd. Thus out of the two given prime numbers, we can have only 2 as the even prime. So now the statement basically states that if we subtract 2 from n, do we end up with a prime greater than 2.

or Is n-2 = a prime greater than 2. Take any odd integer for n. For n=13, we get a YES. For n=17, we get a NO. Insufficient.


Good explanation!

I almost read n to be one of the numbers and did a mental calculation to arrive at C. But, now i am clear!
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Can the positive integer n be written as the sum of two... [#permalink] New post 12 Aug 2013, 02:20
Can the positive integer n be written as the sum of two different positive prime numbers?
1) n is greater than 3.
2) n is odd.
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Re: Can the positive integer n be written as the sum of two... [#permalink] New post 12 Aug 2013, 02:24
Stiv wrote:
Can the positive integer n be written as the sum of two different positive prime numbers?
1) n is greater than 3.
2) n is odd.


1) n is greater than 3.
let n = 8 =5+3 ==>yes
let n = 11 no
not sufficient
2) n is odd
let n= 11 no
let n=5 =2+3..yes
not suffiecient.

combining also with same examples..not sufficient.

hence E
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Re: Can the positive integer n be written as the sum of two... [#permalink] New post 12 Aug 2013, 02:28
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Stiv wrote:
Can the positive integer n be written as the sum of two different positive prime numbers?
1) n is greater than 3.
2) n is odd.


Merging similar topics.

All OG13 questions are here: the-official-guide-quantitative-question-directory-143450.html
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Re: Can the positive integer n be written as the sum of two...   [#permalink] 12 Aug 2013, 02:28
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