How is the minimum percentage calculated for B.Sc. Honours students for BIT MCA entrance test?

No. The official guidelines for BIT Mesra do not specify an upper age limit for the MCA program, provided you meet the educational and percentage requirements. 

Only if already completed. You are eligible if your programme is recognised by DEC-IGNOU and you have already passed the final exam at the time of application. Students currently "appearing" in their final year of a distance learning programme are not eligible to apply.

No you are not eligible for the  BIT MCA program. Only eligible degrees are-
Bachelor of Computer Applications 
OR
B.Sc. in Computer Science 
OR
B.Sc. in Information Technology 
OR
B.Sc. in Computer Applications

Yes. You can apply provisionally. At the time of document verification, you must provide a certificate from your College Principal stating you will complete all examinations by June 2026. Final proof of passing with 55% (50% for SC/ST) must be submitted at the time of admission.

Yes. With a B.Sc. in Mathematics, you are eligible for the BIT MCA program, as long as you meet the minimum percentage requirement and had Mathematics (or CS/IP) in Class 12.