Is it possible to become a business manager after completing B.Sc Maths?

Yes. you can become very good manager. and you have advantage of math. its also advisable do the mba. in marketing or international business. which help you organisation, planning , branding. .this knowledge will give you sharpness.

Yes, there is. You first try to appear for CAT & then depending on score you may search colleges for Business management MBA course.