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# Paper test 42- Prime/Remainder question

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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 $$n^2$$)

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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 ?

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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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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?

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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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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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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

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

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21 Jan 2009, 23:51
Thanks Ian for clarification.

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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!

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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?

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