Hello aspirant, 

For each subject the total of both plus one and plus two is out of 200.And for getting A plus in any subject, you have to score 180 out of 200.And if you consider only the plus two marks it is 72 out of 80 and 90 out of 100.

90 Above 90 percentage is called Aplus.For calculating 90 percent of the total marks, use the following formula

Total marks*0.9

Good luck