For my more advanced students, I have a set of Pythagorean Theorem questions where the lengths of sides are algebraic expressions, rather than just numbers. My students need to demonstrate their aptitude with quadratic expressions.
For example, they should be able to expand (x+4)(x-3).
The solution to this problem is usually written as x2+x-12. But what if the students entered x-12+x2 ? Would Moodle still mark this answer as correct?
At the very least, we need a question type that understands the commutative, associative, and distributive properties. The solution is provided by a Computer Algebra System (CAS). For a general background on computer algebra systems, refer to http://en.wikipedia.org/wiki/Computer_algebra_system.
STACK is a Computer Aided Assessment (CAA) system that overcomes these kinds of mathematical problems. STACK is the brainchild of Chris Sangwin; for more details on STACK, check out the STACK documentation...