Numbers are an interesting and useful device in tracking the tribal and ethnic origins of a document. For example, the Chinese avoid using the number four, which they regard as a bad omen, yet four is a sacred number to the Plains Indians of North America and is used in ceremonies and rites, such as the Vision Quest.
In the Bible we are able to track the origin of some narratives using number symbolism. The Hebrew Bible comes to us from the Afro-Asiatics whose number symbolism can be classified into western and eastern traditions. In the Hamitic-Nilotic tradition the number forty appears often, but forty doesn't appear in the Mesopotamia-Babylonian tradition.
For example, the story of Noah's flood speaks of rain for "forty days and forty nights", but in the Book of Daniel, which is rich in number symbolism, the number forty doesn't appear even once. Noah's homeland was near Lake Chad in west central Africa and the Book of Daniel comes from ancient Babylon.
The number forty in the western tradition relates to the periodic forty day flooding of the Nile when people living near the banks had to leave their homes. The second forty - forty days AND FORTY NIGHTS - relates to the additonal forty days they had to wait for the waters to receed before they could return to their homes. So "the forty days and forty nights" of rain during Noah's flood indicates that this story's origins is not Mesopotamia, but Africa. Likewise Israel's forty years of wandering in the wilderness indicates that this story has roots in Egypt.
Can you think of other numbers in the Bible that help us to track the origins of the narratives?