How is the overall percentage for CBSE 12th calculated?

1) one language and four elective.
2) two language and three elective.
Generally when a school has a provision for 6th subject like Physical Education or Biotechnology, etc. then if a student gets less in any PCM/PCB/PCMB then the marks of sixth subject (if greater than PCM/PCB/PCMB marks) is considered while calculating the percentage.
For Example :
Let us consider a student X’s marks are as follows-
English 85
Physics 89
Chemistry 80
Maths 95
Biology/Comp Sc./I.P. 95
Phy. Ed. 88
Then X’s percentage would be 90.6%
Now Let us consider a student Y’s marks –
English 75
Physics 89
Chemistry 80
Maths 95
Biology/Comp Sc./I.P. 95
Phy. Ed. 88
Then Y’s percentage would be 88.4%