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Number Systems

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Number Systems

by sukhman » Tue Oct 15, 2013 8:27 am
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. tens digit of n is a factor of the units digit of n .
2.the tens digit of n is 2 .
Answer A
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Source: — Data Sufficiency |

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by Brent@GMATPrepNow » Tue Oct 15, 2013 8:46 am
sukhman 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. tens digit of n is a factor of the units digit of n .
2.the tens digit of n is 2 .
Answer A
Target question: Is n composite?

Given: n > 20

Statement 1: The tens digit of n is a factor of the units digit of n
It doesn't take long to list the 2-digit numbers that satisfy this condition:
22, 24, 26, 28
33, 36, 39
44, 48
55
66
77
88
99
All of these possible values of n are composite, so n must be composite.
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: The tens digit of n is 2.
There are several values of n that meet this condition. Here are two:
Case a: n = 21, in which case n is composite
Case b: n = 23, in which case n is not composite
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer = A

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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