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is n composite?

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is n composite?

by sanju09 » Fri Apr 10, 2009 5:56 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) 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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by Nailya » Fri Apr 10, 2009 10:13 am
This can be solved by picking numbers that satisfy the condition given

1) the tens digit of the number is a factor of the units digit.
Lets check those numbers: 21 does not satisfy the condition because 2 is not a factor of 1.
22 - composite
24- composite
all numbers whose factor is 2 are composite numbers
33,36, 39, 44, 48, 55, 66, 77, 88, 99 - these are all numbers that satisfy this condition and they all are composite. Sufficient.

2) the tens digit of n is 2
21 - composite
22- composite
23- prime - not Sufficient.

Therefore, A.
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by cramya » Fri Apr 10, 2009 4:20 pm
Good solution Nailya.
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