I couldn't find an answer to the first question on this page:
http://www.8foxes.com/real-killers

I found a 4th degre polynomial but could not get a solution algebrically.

Even the simple questions at the main page is tricky:
http://www.8foxes.com/

#21 is pretty good!
Also, the one with the slide asking the maximum range is very difficult -I think.

-O