If one does a WeBWorK install from the live DVD, MathJax is set up correctly in the directory .../mathjax. Whoever set up your system must have made changes probably trying to upgrade MathJax. The liveDVD documentation refers people to http://webwork.maa.org/wiki/Installation_Manual_for_2.7_on_Ubuntu_12.04#Checking_for_and_installing_hotfixes where one can find info on MathJax under the section: "Updating MathJax".
Arnie