Dear Ashish

As per CBSE rule, you can calculate your percentage as you have specified in your question. However,

Whether or not Chemistry will be considered towards calculating the final percentage of Class 12, will to a large extent depend upon the type of course you are applying for in undergraduation. 

For instance, if you are applying for an entrance exam or course which considers the marks scored in Chemistry, then you can't eliminate it and keep Kannada as an option. Like, for JEE exam, undergraduation in Biotechnology, etc. 

If in case you are applying for a course which doesn't require Chemistry or has it as a compulsory requirement, then the authorities might allow you to eliminate Chemistry. 

Hope it helps. 

All the best!