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An integer greater than 1 that is not prime is called

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An integer greater than 1 that is not prime is called [#permalink] New post 08 Jan 2008, 05:20
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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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Re: composite number [#permalink] New post 08 Jan 2008, 06:08
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(1) The tens digit of n is a factor of the units digit of n.

If this is true then n is NOT a prime number. This is true because if the tens digit is a factor of the units digit, the whole number will be divisible by that number because the tens digit is obviously a factor of itself! Try it out:

2X = 22, 24, 26, 28
3X = 33, 36, 39
4X = 44, 48
5X = 55
6X = 66
7X = 77
8X = 88
9X = 99

For each of these numbers the tens digit evenly goes into itself and is then a factor of the units. Impossible to have a prime number under these rules. SUFFICIENT

2. Statement 2 tells us nothing on its own. n could be prime (23) or composite (24)

Answer A
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Re: composite number [#permalink] New post 09 Jan 2008, 01:21
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marcodonzelli 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



A.

Stat 1:
If the units digit is not 1 (which it isn't since n>20) and the units digit is divisible by the ten's digit, then n is not prime. Suff.

Stat 2:
22 not prime
29 prime.
Insuff.
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Re: composite number [#permalink] New post 08 Jan 2008, 06:17
i believe it is E

St 1. Not sufficient. Consider 139
St 2. Not sufficient.
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Re: composite number [#permalink] New post 08 Jan 2008, 06:23
Quote:
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?
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Re: composite number [#permalink] New post 08 Jan 2008, 09:49
eschn3am wrote:
Quote:
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?


eschn3am is right....he's always quite good!
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Re: composite number [#permalink] New post 08 Jan 2008, 16:28
Since its only a two digit integer. It must be a composite number.

A.
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Re: composite number [#permalink] New post 27 Feb 2013, 03:43
eschn3am wrote:
(1) The tens digit of n is a factor of the units digit of n.

If this is true then n is NOT a prime number. This is true because if the tens digit is a factor of the units digit, the whole number will be divisible by that number because the tens digit is obviously a factor of itself! Try it out:

2X = 22, 24, 26, 28
3X = 33, 36, 39
4X = 44, 48
5X = 55
6X = 66
7X = 77
8X = 88
9X = 99

For each of these numbers the tens digit evenly goes into itself and is then a factor of the units. Impossible to have a prime number under these rules. SUFFICIENT

2. Statement 2 tells us nothing on its own. n could be prime (23) or composite (24)

Answer A


The ones in red won't satisfy the statement but the rest of the examples are spot on..
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Re: An integer greater than 1 that is not prime is called [#permalink] New post 27 Feb 2013, 05:37
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Re: composite number [#permalink] New post 02 Apr 2013, 08:09
fozzzy wrote:
eschn3am wrote:
(1) The tens digit of n is a factor of the units digit of n.

If this is true then n is NOT a prime number. This is true because if the tens digit is a factor of the units digit, the whole number will be divisible by that number because the tens digit is obviously a factor of itself! Try it out:

2X = 22, 24, 26, 28
3X = 33, 36, 39
4X = 44, 48
5X = 55
6X = 66
7X = 77
8X = 88
9X = 99

For each of these numbers the tens digit evenly goes into itself and is then a factor of the units. Impossible to have a prime number under these rules. SUFFICIENT

2. Statement 2 tells us nothing on its own. n could be prime (23) or composite (24)

Answer A


The ones in red won't satisfy the statement but the rest of the examples are spot on..


The ones in red do satisfy the statement. eschn3am is correct. EX: 2 is a factor of 6 and 8, 3 is a factor of 9
Re: composite number   [#permalink] 02 Apr 2013, 08:09
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