musaafir

Law of safr distance

Q: How can one tell that traveling this much distance reduces to half rakahs of prescribed salah whereas that distance doesn't make them tired and what is the case of traveling less than the prescribed distance and getting more tired, at this situation is there any reduction in rakah of salah. What is the factor which acts main in reduction of number of rakah of salah. Is there any rule if travel one day, stays less than 3-4days and returning back, in this situation can we pray reduced salah or fulfilled salah.