'One fifth' in the Bible

Pharaoh should do this -- he should appoint officials throughout the land to collect one-fifth of the produce of the land of Egypt during the seven years of abundance.

When you gather in the crop, give one-fifth of it to Pharaoh, and the rest will be yours for seed for the fields and for you to eat, including those in your households and your little children."

So Joseph made it a statute, which is in effect to this day throughout the land of Egypt: One-fifth belongs to Pharaoh. Only the land of the priests did not become Pharaoh's.