You need 80% UMS overall and 90% UMS at A2 to get an A*
To get 90% UMS one year you might need 62 marks in the exam and the next year you might need 70 (depending on what the exam is out of). This is because they shift the grade boundaries depending on how well people do, so if one year everyone does badly, you might only need 70% of the exam to get an A*, but this would still give you the same amount of UMS points as another year when it was 85% to get an A*. This makes it impossible to predict how many raw marks you'll need in the exam as you don't know the grade boundaries.
If you got 100% in your coursework, which is 40/100 of your course, out of the remaining 60 available you only need 50 so it adds up to 90/100 (90%).
50/60 x 100=83%
So you need 83% of the UMS points, which is between an A-A* in the exam. But remember, the grade boundaries change so you can't work out how many marks you need in the exam, only that you need roughly a mid A-grade
Don't know if that made any sense, but I hope it did!