Exam

First of all I didn't understand your question, I mean if you are a diploma holder with average 50% marks and have secured a good rank around 50 then you can definitely take admission in KGEC, having maths or not doesn't matters, JELET is basically a exam through which students of diploma engineers can take admission into B.Tech colleges in West Bengal. So, if you are already completed Diploma or in last year then start preparing for it.
GOOD LUCK!

Sure there are many exams like CET, PAT etc.

Hi,Here are some colleges:
1-Department of Management Studies.
2-Narsee Monjee Institute University (MUMBAI).
3-Jaipuria Institute of Management (Lucknow)
4-National Institute of Management. (Calcutta)
5-Christ University, Bangalore
6-IILM, Institute for Higher Education
7-Symbosis International University.

You should have PCM Marks in class 12th and IMU rank. https://www.himtcollege.com/course-details/btech-marine-engineering

No, JEE is not required, admission is merit based.

NATA exam is compulsory for admission in B.Arch in most of the colleges in India. You can also give JEE Mains paper 2 exam for getting good colleges for B.Arch.

Hello,
Please visit this college predictor this will help you to choose best for you
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
Thank you.

You need to have Physics, Chemistry, Biology / Biotechnology and English, as mandatory subject in class 12th. You need to have minimum 50% marks in class 12th. Also, your age should be above 17 years.