Building on a sketch by cwinske, http://www.geogebratube.org/material/show/id/35118
Which Craig posted at http://approachinfinity.blogspot.com/2013/04/geogebra-help.html
It's a very nice idea, to be able to move points and see the effects on the mean and median.
I added a guessing game for the mean. (Which may be too grudging with its praise.)
