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An integer greater than 1 that is not prime is called [#permalink]
 10 Sep 2008, 01:05
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An integer greater than 1 that is not prime is called composite. If the two-digit 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.
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dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the two-digit 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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gmatnub wrote: dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the two-digit 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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Manager
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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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dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the two-digit 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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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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Manager
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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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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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guys, do we have an OA? A & C are very temptative ...........
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OA is A. Bin 4 problem.
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What is the source of these problems ?
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dancinggeometry wrote: An integer greater than 1 that is not prime is called composite. If the two-digit 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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dancinggeometry wrote: OA is A. Bin 4 problem. Whats the source of these questions ?
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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
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