Complex sentence: Their best-known means of livelihood is semi-nomadic reindeer herding, with which about 10% of the Sami are currently connected and 2,800 actively involved on a full-time basis.
Split into simpler sentences: Their best-known means of livelihood is semi-nomadic reindeer herding. Currently about 10% of the Sami are connected to reindeer herding and 2,800 are actively involved in herding on a full-time basis.