Wat is the duration of the CA(Charted Accountant)?

It would be a good idea to pursue it along side B.Com. Based on the new curriculum, CA will take around 3.5 years to complete. If you are really interested in commerce then you should not be worried about the percentage. There is no hard and fast rule that high scorers should only go for courses like medicine and engineering. If you have an interest in going towards commerce and accounting then its a good stream to go into. With regard to keeping Math as an optional subject, if you are good at it, then sure you can. CA is one of the few professional courses which opens up avenues for both private practice as well as a corporate career. With good marks and good percentages you can definitely do well in the course.