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Bunuel
If z is a positive integer, is \(\sqrt{z}\) an integer?

(1) \(\sqrt{3z}\) is an integer.
(2) \(\sqrt{4z}\) is not an integer.

\(\sqrt{z}\) will only be an integer if \(z\) is a perfect square {4,9,16,25,36,49,etc...}.

(1) \(\sqrt{3z}\) is an integer. Then, z must be a multiple of 3 multiplied by a perfect square, which makes z not a perfect square and \(\sqrt{z}\) not equal to an integer, sufficient.

(2) \(\sqrt{4z}\) is not an integer. Then, z is not a perfect square, because if it was, then the \(\sqrt{4z}\) would be an integer, sufficient.

(D) is the answer.
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If z is a positive integer, is \(\sqrt{z}\) an integer?

(1) \(\sqrt{3z}\) is an integer.
So \(\sqrt{3}*\sqrt{z}\) is an integer. This is possible only when \(\sqrt{z}=\sqrt{3}*y\), where y is an integer.
Thus \(\sqrt{z}\) is a product of an integer and an irrational number, making it a non-integer.
Sufficient

(2) \(\sqrt{4z}\) is not an integer.
\(\sqrt{4z}=2*\sqrt{z}\)=not an integer.
So, \(\sqrt{z}\) is not an integer.
Sufficient

D
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