EDIT:Oops I just realised that this is not based on a particular uni. My post was in reference to UNSW. BUt anyway for future reference:
Depending on what course you are doing, you may have the option of doing MATH1131.
Now an overview of MATH1131 and MATH1141:
http://www.handbook.unsw.edu.au/undergraduate/courses/2014/MATH1131.html
http://www.handbook.unsw.edu.au/undergraduate/courses/2014/MATH1141.html
Look at the requirement of Mathematics 1A (MATH1131) you only are expected of getting a combined mark of 100/150 in 3-unit.
Looking at Higher Mathematics 1A (MATH1141), the expectation is 175/200 combined in MX1 and MX2.
If you have the option, I suggest you do Mathematics 1A (MATH1131) first semester, and if you get a high distinction in that, consider doing Higher Mathematics 1B (MATH1241) for semester 2.