Right. I know how to get to a right answer but didn't understand Tordmor's expression.
Starting with
substitute one into the other to eliminate it
simplify
then solve for ball
then compute
This is literally how I would solve this problem. So you can see why I'm surprised people can answer it correctly on the fly.
http://psychcentral.com/news/2011/09/21/cognitive-style-tends-to-predict-religious-conviction/29646.html
I think this is the source but I can't be sure:
http://www.apa.org/pubs/journals/releases/xge-ofp-shenhav.pdf
http://lesswrong.com/lw/7o4/atheism_autism_spectrum/4vbc
Reddit /r/psychology discussion