Hello deepan

For joining PSUs

Bsc in maths is not sufficient, you need to to atleast do masters and PhD to get job in ISRO or any equivalent organisations.

But as you are from Bsc maths, you have really a big opportunity in front of you, as mathematics plays important role in real world, all the IT sector companies, who are hiring data mining, data analysts and there are many other companies who hire students from mathematics background, if your maths is good you can do a course which is in trend right now, and you can get placed with a very good package overall, and also there are many civil services you can try( many civil services have a good portion of mathematics and general knowledge),a student good in maths have no problem in real world.

I hope it helps

Hello

With BSc, you will get job at schools as a teacher. You have to pursue MSc in maths specialization so that you can apply for different education institutes and universities.  for private sector and public sector, you have public or private educational institutes to join. You can do MSc at IIT at any campus which is highly recognized and you can do PhD too if you want and do a job at an IIT campus or other campus.

Hope it helps!