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An integer greater than 1 that is not prime is called [#permalink]
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10 Sep 2008, 01:05
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An integer greater than 1 that is not prime is called composite. If the twodigit integer n is greater than 20, is n composite? (1) The tens digit of n is a factor of the units digit of n. (2) The tens digit of n is 2. == Message from GMAT Club Team == This is not a quality discussion. It has been retired. If you would like to discuss this question please repost it in the respective forum. Thank you! To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative  Verbal Please note  we may remove posts that do not follow our posting guidelines. Thank you.



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 01:44
dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the twodigit integer n is greater than 20, is n composite?
(1) The tens digit of n is a factor of the units digit of n. (2) The tens digit of n is 2. C the number is even not a because the number can be 24 or 113



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 05:06
gmatnub wrote: dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the twodigit integer n is greater than 20, is n composite?
(1) The tens digit of n is a factor of the units digit of n. (2) The tens digit of n is 2. C the number is even not a because the number can be 24 or 113That is not true. n is a two digit integer greater than 20....hence A should be sufficient.



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 05:15
IMO A.
(1) The tens digit of n is a factor of the units digit of n >
lets consider the number is 10X +y ; it says Y=kX.. so the number will becose 10X+KX = X (10 +k) which will be a composite number unless X=1 ; now X can not be 1 as 10X+Y> 20
also if you read this option properly the, number shoul be 10X+Y < 49
(2) The tens digit of n is 2.



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 12:46
dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the twodigit integer n is greater than 20, is n composite?
(1) The tens digit of n is a factor of the units digit of n. (2) The tens digit of n is 2. Good question! Basically this question want to know whether n is prime. Let's assume that n = 10a + b 1) Since b = ax, n = 10a + ax = a*(10+x) n cannot be prime because it has more than one factor. Or n is a composite. SUFF 2) n = 20 + b b can be any number from 1 to 9. Some are prime and some are composite. INSUFF



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 12:46
I got A as well but I had to think through it.
(1) The tens digit of n is a factor of the units digit of n.
If 9, factors are 9,3,1 = 19,39,99 If 8, factors are 8,4,2,1 = 18,28,48,88 If 7, factors are 7,1 = 17,77 If 6, factors are 6,3,2,1 = 16,26,36,66 If 5, factors are 5,1 = 15,55 If 4, factors are 4,2,1 = 14,24,44 If 3, factors are 3,1 = 13,33 If 2, factors are 2,1 = 12,22 If 1, factors are 1 = 11
None of the # above 20 are prime, so it is composite.



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 14:10
A
(1) The tens digit of n is a factor of the units digit of n. ex: any number greater than 20, and tens digit is a factor of the units digit. 24, 26, 28, 36,33....none r prime...so they have to be composite
So, A is sufficient
(2) The tens digit of n is 2. ex: 21,22,23,24,25....could be prime or composite
So, B is not sufficient...



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Re: Zumit DS 015 [#permalink]
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10 Sep 2008, 23:07
Good question indeed ... I decided the answer was C before reading through the solutions below... I guess I need to be more careful with DS ....
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Re: Zumit DS 015 [#permalink]
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11 Sep 2008, 01:30
guys, do we have an OA? A & C are very temptative ...........



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Re: Zumit DS 015 [#permalink]
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11 Sep 2008, 02:39
OA is A. Bin 4 problem.



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Re: Zumit DS 015 [#permalink]
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11 Sep 2008, 03:10
What is the source of these problems ?
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Re: Zumit DS 015 [#permalink]
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14 Sep 2008, 04:53
dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the twodigit integer n is greater than 20, is n composite?
(1) The tens digit of n is a factor of the units digit of n. (2) The tens digit of n is 2. 1) answers since n=10p+q and p is a factor of q n=10p+pm div by p COMPOSITE SUFFI 2)23 is a prime 24 is a composite INSUFFI IMO A
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Re: Zumit DS 015 [#permalink]
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14 Sep 2008, 04:55
dancinggeometry wrote: OA is A. Bin 4 problem. Whats the source of these questions ?
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Re: Zumit DS 015 [#permalink]
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14 Sep 2008, 16:11
spriya wrote: dancinggeometry wrote: OA is A. Bin 4 problem. Whats the source of these questions ? With A, the values can be only 22,24,26,28,33,36,39,44,48,55,66,77,88,99 All these are composite. We have a Yes, Suff With B, 21,22,23 We have yes and no. Insuff hence A == Message from GMAT Club Team == This is not a quality discussion. It has been retired. If you would like to discuss this question please repost it in the respective forum. Thank you! To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative  Verbal Please note  we may remove posts that do not follow our posting guidelines. Thank you.










