Okay, thats fine. The reason i asked is because if you look
here under NCCW(s) - which stads for 'Not to Count for Credit With' - which means if you have completed any units/requirements under this section, you undertaking MATH123 would not count those 3 credit points towards your degree, so it would essentialy be a waste of time.
I believe this unit essentially goes through the useful parts of the 2 unit HSC Maths course.
Since you did General Maths, you're fine to do this - and this can count as a 'planet' unit that is outside you're faculty (i believe) - (Remember you need to complete a 'people' and a 'planet' unit, one being outside your faculty one outside your department).
ECON131 on the other hand is "recommended for students who have completed HSC-level mathematics and need to extend their knowledge of mathematical techniques to applications in business, economics and finance". Note that although it says this can be a 'planet' unit - it is within the Department of Economics in the Faculty of Business and Economics - and so you cant claim it as your 'plpanet' unit.
[If you do choose ECON131 and need a planet unit outside your Faculty,
STAT170 would be useful]
So there is some info for you, it is up to you to decide.
EDIT: Just checked your
Degree Rules and STAT170 is compulsory for you.