How many times was Ruth married in the Bible?

Answer 1

Twice.

Initially Ruth and her sister Orpah were married to Mahlon and Chilion (not necessarily in that order), who were sons of Naomi. When Naomi's husband Elimelech died and the two sons died, the three ladies were left widowed. (cf. Ruth 1:1-6)

Naomi decided to go back to Bethlehem, and Ruth chose to accompany her, while Orpah stayed behind in Moab.

Ruth then meets Boaz, and they marry. They have a son Obed, who in turn has a son Jesse, who then has a son David. Thus Ruth is the great grandmother of the same David who slew Goliath, and later became King David who united Israel. (cf. Ruth 4:17)