'Thirty' in the Bible

Then Abraham said [to Him], “Oh, may the Lord not be angry, and I will speak; suppose thirty [righteous people] are found there?” And He said, “I will not do it if I find thirty there.”

thirty milking camels with their colts, forty cows, ten bulls, twenty female donkeys, and ten [donkey] colts.

Now Joseph [had been in Egypt thirteen years and] was thirty years old when he stood before Pharaoh, king of Egypt. Joseph departed from the presence of Pharaoh and went through all the land of Egypt [performing his duties].