In ICSE Class 10, there are ten subjects. But you have to reduce them into 6 main heads.
English language and English literature are regarded as only English. English marks are average of these two subjects.
Biology, Chemistry and physics are regarded as Science

History and Geography are regarded as Social Science 

Apart from these, other main subjects are Commerce, Physical Education,

Computers, Economics, Hindi/ Regional language (second language)

and last is Math.
Out of these six subjects, while calculating the percentage, you can not skip English marks (it is compulsory) and best four of remaining five subjects. This is also known as the best five system.

For CBSE Class 10 Best of five subjects are:

1. English compulsory

2. Hindi compulsory,
3. Math
4. Science,
5.Social Studies,
6. Any one optional subject lie Phy Edu, IT will also be added.                                            7. A third language will be added from 2018.

For SSC Class 10 Best of five subjects are: 
1.English is Compulsory And select other 4 subjects from the below

2.Mathematics (Algebra & Geometry combined)

3.Marathi

4.Social Studies

5.Science (Paper 1 and Paper 2)

6.Hindi/German Composite

In IGCSE you can skip 2 subjects out of these 7 subjects
1. English is compulsory in both Groups

(science group)
2. Maths
3. Biology
4. Chemistry
5. Physics
6. 2nd language( HINDI, FRENCH, and the language around your area)
7. Food and nutrition

(commerce group)
2. Business studies
3. Accounts
4. Economics
5. Maths
6. Computer science
7. 2nd language ( HINDI,FRENCH, the language around your area)