Economics

Yes, you can join for graduation in Economics. Alternatively you can also enroll for BCA / B.Sc CS if you are interested in computers.

Yes you can apply in delhi university though chances for admission are a bit tough for general category.

Sonu other than B.Sc Economics you can go for B.Com (H), B.Com (Professional), BBA with different specializations). These days we have integrated/ dual courses like B.Com-M.Com, B.Com-MBA, BBA-MBA, etc which are more beneficial than simple/ pass courses.
There are many good universities that are offering all these courses. Most of these universities have good placements and some even offer good scholarships.
Check the websites of some good universities.
Good luck.

UPES conducts its own entrance for MA Economics admission. Entrance is called 'UPESEEE'. This is a completely online test with no pen paper version. The unique feature of this test is that the aspirant can take the test from any convenient location with a net connected PC and a webcam, be it your home, office or even a cyber café. .
Registrations are open for its 2nd round of of MA Entrance and today is last date to register for it so hurry up and apply today.

yes you can take it but you need to give more importance in maths and economics paper which accounts for getting good marks.

You need to prepare for CAT exam from TIME, IMS coaching when you are in the third year. You find difficulties in solving CAT papers of previous years, you need the help of Arun Sharma CAT books , and you must study your papers in graduation. You just need four hours to seven hours a day for CAT study. Best of luck.

Eligibility criteria varies from university to university. Some, like University of Hyderabad, demand a degree in economics to apply for a master's degree while other colleges like DSE & UPES also lets B.com graduates and people with Maths, Statistics etc. to sit for the entrance. DSE and UPES are best bet open for you for MA Economics. Both of these are very good for Economics. This year 100 % batch got placed through campus recruitment in UPES. You can visit websites of respective universities and get the details about exams, eligibility and test dates and apply for the same.