Which b-school for MBA gives admission to students not having aggregate marks of 50%? Which one is best of them?

There is no dearth of useless colleges offering all types of degrees. At least you have 48% but even if had 35%, you would find many colleges. But take advice of @Mahesh. Fact remains that you did not study well and did not work hard. Improve these two qualities.

appear for mat and get into the top collges un dr mat such as iilm, christ,itm etc

Nipunj you need to check out colleges coming under MAT or MAHCET. Doing postgraduate is good option but you can also do M.B.A by working somewhere , getting the experience and then applying for M.B.A.In that case you can get good colleges .

colleges running under the distance education gives admission in less than 50% marks. Some PGDM running colleges also provide the admission at lower percentage.

Nipunj...I will strongly advice you to do a postgraduate degree in a related but easier subject and try to get first class. Only then, you will have a good chance of getting admission in a good business school. With 48% marks, you will only get admission for MBA in a rubbish business school. Have I