If n and k are positive integers, is \sqrt{n+k} > 2\sqrt{

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If n and k are positive integers, is
$$\sqrt{n+k}>2\sqrt{n}?$$
$$\left(1\right)\ k>3n$$
$$\left(2\right)\ n+k>3n$$
The OA is A.

I think that it can be solved as follows:
$$\left(\sqrt{n+k}\right)^2>\left(2\sqrt{n}\right)^2\ \Rightarrow \ n+k\ >2n\ \Rightarrow \ k>3n.$$
Hence, statement 1 is sufficient.
Source: — Data Sufficiency |

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by Jay@ManhattanReview » Wed Jul 18, 2018 3:12 am

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swerve wrote:If n and k are positive integers, is
$$\sqrt{n+k}>2\sqrt{n}?$$
$$\left(1\right)\ k>3n$$
$$\left(2\right)\ n+k>3n$$
The OA is A.

I think that it can be solved as follows:
$$\left(\sqrt{n+k}\right)^2>\left(2\sqrt{n}\right)^2\ \Rightarrow \ n+k\ >2n\ \Rightarrow \ k>3n.$$
Hence, statement 1 is sufficient.
Statement 2 is insufficient since n + k > 3n => k > 2n.

From the inequality k> 2n, we cannot be sure whether k> 3n. It may or may not be. Insufficient.

The correct answer: A

Hope this helps!

-Jay
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