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# An integer greater than 1 that is not prime is called

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VP
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An integer greater than 1 that is not prime is called [#permalink]

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: an-integer-grater-than-1-that-is-not-prime-is-called-88255.html
[Reveal] Spoiler: OA

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Director
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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)

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Manager
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08 Jan 2008, 06:17
i believe it is E

St 1. Not sufficient. Consider 139
St 2. Not sufficient.

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Director
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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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VP
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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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CEO
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08 Jan 2008, 16:28
Since its only a two digit integer. It must be a composite number.

A.

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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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Director
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27 Feb 2013, 03:43
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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)

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]

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27 Feb 2013, 05:37
Expert's post
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OPEN DISCUSSION OF THIS QUESTION IS HERE: an-integer-grater-than-1-that-is-not-prime-is-called-88255.html
_________________

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Intern
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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)

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

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Re: composite number   [#permalink] 02 Apr 2013, 08:09
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