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is sqroot(n) a prime number?

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Source: — Data Sufficiency |
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by neelgandham » Tue Dec 13, 2011 3:41 pm
If n is an integer, is sqroot(n) a prime number?
(1) n - 2 is a prime number.
If n = 9, then n - 2 = 7(prime) and sqroot(n)=3 (Prime)
If n = 7, then n - 2 = 5(prime) and sqroot(n)= Non-Integer (Non Prime)
Two different answers, hence Insufficient!
(2) n^2 is not a prime number.
Assuming n2 = n^2,
n^2 is never a prime number, and satisfies all the real numbers on the number line.
So again considering two numbers on the number line.
If n = 9, then n - 2 = 7(prime) and sqroot(n)=3 (Prime)
If n = 7, then n - 2 = 5(prime) and sqroot(n)= Non-Integer (Non Prime)
Two different answers, hence Insufficient!

IMO E

Let me know if you are looking for a different approach!
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by Anurag@Gurome » Tue Dec 13, 2011 7:59 pm
venmic wrote:If n is an integer, is sqroot(n) a prime number?

(1) n - 2 is a prime number.
(2) n2 is not a prime number.

E

what is the fastest way to do this
As explained by Neelgandham, picking numbers approach will be a good approach for these types of questions.
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