Tip request for unfinished topic in exam

[mcrudo]

Genreal question:
is it better to leave a question unanswered in multi choice section or in the dying seconds have a quick educated guess?
How does the score get counted for unanswered questions?
e.g. if you are very slow + have 4 Q's left in a section and randomly select a,b,c,d you have a chance of hitting correct answers rather than no chance?

[Tinkers]

It's always a good idea to have a guess. No marks are taken away etc.