Benni wrote:Hi Guys,

regarding OG 13, 157, Data Suffiency.

If n is a positive integer and k=5.1x10^n, what is value of k?
(1) 6000<k<500 000
(2) k²=2.601x10^9

OA is D.


What I dont get is. k²=2.601x10^9. Therefore k=Plus or Minus Squareroot of 2.601x10^9. So in my view 2 is not sufficient. My question therefore is: When do I have to take account of the negative square root and when do I ignore it.

Thanks

Benni wrote:Thank you for your very quick reply. I appreciate it. Your explaination is just fantastic.

But if you could please take a look at OG 13, 167, Datasufficiency:

If n and k are positive integers, is sqrt(n+k) > 2sqrt(n)?
1) k > 3n
2) n + k > 3n
OA is A.

They square the inequality to n+k>2n saying n and k are positive.
But what about following example: sqrt9>sqrt 4? --> solution one 3>2 and solution two -3>-2.
Now by squaring the solution b is lost. And this drives me crazy. Why are we allowed to square here.

Thank you very much.
Ben