They are the same thing. Exam. is a shortened version of examination made so for convenience
Test examination is a work given to a scholar in the class for which he is assigned marks, while assignment is a work given to the scholar to do at home and show it on the class specified.
difference between as on and as at
No correlation. The mark you get in your exam, relates to the number of correct answer you have given. It has nothing to do with your class attendance.
The difference is 2,795.
Directly. Their difference IS the difference between them.