'Forty Years' in the Bible

so that in forty years there shall no foot of man walk there, neither foot of cattle go there, neither shall it be inhabited.

I will make the land of Egypt to be desolate among other waste countries, and her cities to lie void forty years, among other void cities: And I will scatter the Egyptians among the Heathen and nations.

Again, thus sayeth the LORD God: When the forty years are expired I will gather the Egyptians together again, out of the nations, among whom they were scattered,