Hi Dinesh,

The eligibility criteria for RBI grade B (DSIM) post is

Master's Degree in Statistics/ Mathematical Statistics/ Mathematical Economics/ Econometrics/ Statistics & Informatics from IIT-Kharagpur/ Applied Statistics & Informatics from IIT-Bombay with a minimum of 55% marks or equivalent grade in aggregate of all semesters/years;

OR

Master's Degree in Mathematics with a minimum of 55% marks or an equivalent grade in aggregate of all semesters/years and a one-year post-graduate diploma in Statistics or related subjects from an Institute of repute;

OR

M. Stat. Degree of Indian Statistical Institute with a minimum of 55% marks in aggregate of all semesters/years;

OR

Post Graduate Diploma in Business Analytics (PGDBA) jointly offered by ISI Kolkata, IIT Kharagpur, and IIM Calcutta with a minimum of 55% marks or equivalent grade in aggregate of all semesters/years.

Now looking at this you belong to  the second category with a post graduate in maths you need an additional one year post graduate diploma in statistics or related field from a reputable institute. Note reputable because other requirements have IITs and IIMs in it!

Hope this info is helpful.

All the best!