A. (by #DrZakirNaik): According to hadith of our beloved Prophet Muhammad (peace be upon him) which says, “start your fast with the people who are starting the fast and break the fast when the people around you break the fast”. So if he lives in Saudi Arabia he should start his fast with the people of Saudi Arabia and if in between in Ramadan he goes back to his original home in India then he should fast till the time his people are fasting. And I am aware many times there is a difference of couple of days. So if he starts his fast two days earlier and he goes to India. By the time he finishes his 30 fasts the people of India may still have 1 or 2 fasts left. But yet he has to continue fasting with the people of India even if it exceeds more than 30 days.
Now If it is vice versa i.e. if he starts fasting in India (i.e. 2 days late) then comes to Saudi Arabia then maybe he will fast only 28 days. In this case he has to start with people of India and end with the people of Saudi Arabia and he cannot fast on the EID day because that is haraam. But after that he has to fast at least 1 day to complete his 29 days because a lunar month is at least 29 days. So he should fast 1 or 2 days after EID so that he does not fast less than the minimum requirement.