root (.0026) = root(26)/root(10000) = root(26)/100 = ~5/100 = ~.05

It cannot be .06 as that would required the value in question to be root(.0036) or something very close.

Hope this helps.

I think the best way to do this one is to estimate. You should know that the square root of 25 is 5. So, since this is very close to the square root of .0025, the answer must be .05. Also, as pointed out, it's useful to know that it can't be any of the answers ending in 6 because that puts it closer to 36 than to 25.

Another way to do it is to work backwards, by squaring the answer choices. If they yield .0025, that's the answer.

If we take .05*.05, we get .0025. Try squaring the other answer choices, and they are way off.

Hope this helps!

I like the answers given, but if you decide to "plug numbers", you should do it intelligently, after some consideration since squaring some answer choices (not necessarily these) could be a little hairy.

My point is to start with your best guess rather than just moving from A to E sequentially until you find what you're looking for.