MBA/PGDM

You need not to learn basics of commerce for MBA entrance.
Almost every MBA entrance exam's syllabus is as follows:-
Verbal ability and reading comprehension: This section of the exam paper determines the grasp a candidate has on English language. The question paper will comprise of passage, and questions based on the passage. Through this section, a candidates vocabulary, grammar, synonyms, antonyms, sentence completion, comprehension is tested. To answer the questions, the candidate must first understand the contents of the passage, and secondly, use correct phrases, words and expressions. Quantitative aptitude: This section of the paper assesses a candidate's ability to solve numerical calculations with speed and accuracy. To excel in this section, the candidate must have a good understanding of ratio and proportion, percentage, interpretation of tables, charts and graphs.
Logical / abstract reasoning: This section determines a candidate's ability to think quickly and accurately. Candidates can expect questions on verbal reasoning or on diagrams and figures in this section.

The following is my opinion after following NSE, BSE, NISM and Indian Stock Markets since past many years and also after undertaking various NISM, NCFM and BCFM exams:
History of NCFM:
NSEs Certifications in Financial Markets (NCFM) are practical oriented examinations developed by NSE. The primary objective of having NSEs Certifications was to ensure a bare minimum knowledge about the financial products, trading systems, etc. And therefore, these certifications were made mandatory by NSE prior to registering its members on the stock exchange. Besides, NSE, as a stock exchange also wanted to educate the securities market participants and the Indian community as a whole about various aspects of Indian Stock Market. They started this initiative on a large scale in the form of NCFM Certifications and were successful in doing so. However, considering the fact that Indian market participants were not so mature and professionalized, the level of difficulty for most of NCFM Certifications were kept at a low level. Soon, it becomes very easy for people to clear these certifications easily. Why NISM was born?
As the number of NCFM exam takers went up, NSE saw these certifications as a money minting machine and decided to continue with its low difficulty level. Other stock exchanges, namely, BSE, MCXSX (now MSEI) also launched similar certifications and made it mandatory for their members to have these certifications before registering on their respective stock exchange. Soon, SEBI sensed that brokers/members were now required to undertake multiple certifications to register themselves on the stock exchange, I.e., NCFM Certification for NSE and BCFM Certification for BSE and so on. SEBI, therefore, took this initiative of having a common certifying body for certification of people working in Indian securities markets and NISM was assigned this responsibility.
Thus, NISM Certifications was born in 2009. What are NISM Certifications? NISM Certification Examinations are the most authentic, practical and mandatory Certifications available for various areas of Indian securities market. The Certifications are mandated by SEBI under SEBI (CAPSM) Regulations, 2007 which itself gives them the necessary credibility. What this means is that all brokers, members, mutual fund distributors, traders, dealers and other market participants who were earlier required to pass the exchange level examination (i.e., NCFM, BCFM, etc.) are now required to pass a single NISM Exam.

Hello Ajish,
The information you have given is quite interesting. You have scored quite well in your 10th, your 12th and even in your MBA. But while doing BE, something has happened which made you not score well. Oh. After you have finished MBA now you want to do Masters in mechanical engineering? Is that right? Yes, you can of course do it because you have scored more than 50%. You need to appear for GATE and depending on the marks obtained in GATE you can get an engineering college.
Normally speaking, your marks in BE should not matter much as compared with what you will get in GATE 2019, but which college and which university you will get depends to a large extent on how those scored better than you give their choice. So I suggest you should not think over it and just concentrate on clearing GATE2019, with very good marks to get admission in your desired college.