to do this the question i understand and than do the other questions after?
Yea, that seems more practical to not waste time. Whenever I do an exam, like for science or maths I always do the ones I know first so I can secure those few marks before moving onto harder questions
to do this the question i understand and than do the other questions after?
That is sensible, but for me I find that I always avoid the questions where I have to write more and then, don't leave myself time at the end. I'm not sure whether you have that problem, but you may avoid questions because you want to do it rather than you don't understand.