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Number System 3

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Number System 3

by ranjeet75 » Fri Feb 03, 2012 9:46 pm
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.

Please elaborate the method to solve the ques
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by Anurag@Gurome » Fri Feb 03, 2012 9:54 pm
ranjeet75 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.

Please elaborate the method to solve the ques
(1) The tens digit of n is a factor of the units digit of n and n > 20 implies that the possible values of n can be 22, 24, 26, 28, 33, 36, and 39 (as the units digit can be 2 * 1 , 2 * 2 , 2 * 3 , 2 * 4, 3 * 1 , 3 * 3). So n is composite; SUFFICIENT.

(2) The tens digit of n is 2 implies that the possible numbers can be from 20 to 29, out of which some are prime numbers while other are composite. So, n may or may not be composite; NOT sufficient.

The correct answer is A.
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