Hi Nick
thank you for your contribution to Moodle
i tried to understand your creation but i don't understand how it is different to a standard moodle "calculated question" type.
e.g. in moodle you can do the same thing: create two variabes; {apples1} and {apples2}
and then create a question like: John as {apples1} apples, and he eats {apples2} apples. How many does he have left?
i don't understand what your plug in does per se that isn't already being done?
chrs
BK