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# Paper test 42- Prime/Remainder question

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Senior Manager
Joined: 25 Nov 2006
Posts: 333
Schools: St Gallen, Cambridge, HEC Montreal
Paper test 42- Prime/Remainder question [#permalink]

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18 Jan 2009, 06:35
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If n is a prime number greater than 3, what is the remainder when $$n^2$$ is divided by 12?

A - 0
B - 1
C - 2
D - 3
E - 5

x2suresh - I updated the question (change from n to $$n^2$$)
Senior Manager
Joined: 25 Nov 2006
Posts: 333
Schools: St Gallen, Cambridge, HEC Montreal
Re: Paper test 42- Prime/Remainder question [#permalink]

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18 Jan 2009, 06:39
If n=13, the remainder is 1

If n=17, the remainder is 5

Has anyone got the ?
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1346
Re: Paper test 42- Prime/Remainder question [#permalink]

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18 Jan 2009, 07:32
lumone wrote:
If n is a prime number greater than 3, what is the remainder when n is divided by 12?

A - 0
B - 1
C - 2
D - 3
E - 5

Yes, the question doesn't make any sense as written; there will be different answers for different values of n.
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Senior Manager
Joined: 25 Nov 2006
Posts: 333
Schools: St Gallen, Cambridge, HEC Montreal
Re: Paper test 42- Prime/Remainder question [#permalink]

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18 Jan 2009, 14:10
IanStewart wrote:
lumone wrote:
If n is a prime number greater than 3, what is the remainder when n is divided by 12?

A - 0
B - 1
C - 2
D - 3
E - 5

Yes, the question doesn't make any sense as written; there will be different answers for different values of n.

But this is a question from an official retired gmat test... The question is supposed to make sense

Anyone?
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1346
Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 01:29
lumone wrote:
IanStewart wrote:
lumone wrote:
If n is a prime number greater than 3, what is the remainder when n is divided by 12?

A - 0
B - 1
C - 2
D - 3
E - 5

Yes, the question doesn't make any sense as written; there will be different answers for different values of n.

But this is a question from an official retired gmat test... The question is supposed to make sense

It very clearly is not a question from an official test, because it doesn't make sense. I have test code 42, and this question isn't in it; maybe you could tell us where you saw it (test code, section and question number).
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Joined: 04 May 2006
Posts: 1830
Schools: CBS, Kellogg
Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 02:31
lumone wrote:
If n is a prime number greater than 3, what is the remainder when n is divided by 12?

A - 0
B - 1
C - 2
D - 3
E - 5

12+0=12
1+12=13
2+12=14
3+12=15
5+12=17

Clearly A, C and D out, only B and E remains

Test with the quotient=0
12*0+1=1
12*0+5=5

1 cannot be a prime, so E must be the answer
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Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 05:02
sondenso wrote:

Test with the quotient=0
12*0+1=1
12*0+5=5

1 cannot be a prime, so E must be the answer

1 isn't relevant; the question says that n is greater than 3. If n is prime, the remainder can be 1, 5, 7 or 11 when you divide n by 12.
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Senior Manager
Joined: 25 Nov 2006
Posts: 333
Schools: St Gallen, Cambridge, HEC Montreal
Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 05:25
It's a question from Test code 37 - Section 1 - Question 4

Manager
Joined: 04 Jan 2009
Posts: 236
Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 10:27
lumone wrote:
It's a question from Test code 37 - Section 1 - Question 4

certainly a tricky question. I can come up with possibilities like 13, 37, etc. How can you rule 1 out?
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tusharvk

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Re: Paper test 42- Prime/Remainder question [#permalink]

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19 Jan 2009, 13:13
I'm not sure if you're looking at the original version of the test, but the actual question is this:

If $$n$$ is a prime number greater than 3, what is the remainder when $$n^2$$ is divided by 12?

0
1
2
3
5

That's a question with an answer.
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Joined: 17 Jun 2008
Posts: 1507
Re: Paper test 42- Prime/Remainder question [#permalink]

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21 Jan 2009, 23:51
Thanks Ian for clarification.
Manager
Joined: 13 Jan 2009
Posts: 168
Re: Paper test 42- Prime/Remainder question [#permalink]

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22 Jan 2009, 21:59
This one is more clear. Thank you Ian!
Director
Joined: 29 Aug 2005
Posts: 836
Re: Paper test 42- Prime/Remainder question [#permalink]

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24 Jan 2009, 11:37
Although, iteratively one can arrive at a remainder of 1, what is the logic behind it?
Manager
Joined: 04 Jan 2009
Posts: 236
Re: Paper test 42- Prime/Remainder question [#permalink]

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24 Jan 2009, 16:40
botirvoy wrote:
Although, iteratively one can arrive at a remainder of 1, what is the logic behind it?

you can prove this mathematically; but may be beyond the scope of this question.
This does bring up interesting point. Are we supposed to remember such properties of numbers or should we derive at the time of exam or just do by method of substitution at the time of exam?
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tusharvk

Re: Paper test 42- Prime/Remainder question   [#permalink] 24 Jan 2009, 16:40
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# Paper test 42- Prime/Remainder question

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