Student or Learner
1. The use of comma before coordinator "and"...Sometimes I see without comma and sometimes with comma...Which is right for Business English?
2. 2. The use if comma before words of transition is wrong but why is semi-colon fine?
1-- to be sure, use the comma. It is sometimes omitted in the case of short clauses.
2-- That is simply their nature: a transition distances the statements somewhat. I presume you have found the list of transitional conjunctions that are preceded by a comma.