Peter Norvig covered STUDENT (http://en.wikipedia.org/wiki/STUDENT_(computer_program)), a program that solves algebra word problems, in "Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp" back in 1992.
Perhaps also of interest in this context is the work of Gordon Novak (http://www.cs.utexas.edu/users/novak/) in the 1970s, related to AI/NLP interpretation of elementary physics problems [1].