Bible Contradiction Du Jour: How long were the Israelites in Egypt?
Several places in the Bible claim they were there 400 years or longer, but the numbers don't add up. From The Skeptical Reveiw:
This genealogy, along with its parallels in I Chron. 6:1-3 and 23:6-13, establishes that Moses was the great grandson of Levi. Kohath, the grandfather of Moses, had already been born when Jacob took his sons and their families into Egypt, (Gen. 46:11). If we assume that Kohath was only a suckling infant in his mother's arms when he was taken into Egypt and if we further assume that his last act on earth at the age of 133 (Ex. 6:16) was to sire Amram, the father of Moses, then the very latest date of Amram's birth would have been around 134 years into the Israelite sojourn. If we then make similar assumptions about the birth of Moses, i.e., that Amram sired him just before dying at the age of 137 years (Ex. 6:20), this would mean that Moses could have been born no later than 272 years after the Israelite sojourn began. Since Moses was only 80 years old when Jehovah (Yahweh) called him to lead the Israelites out of Egypt (Ex. 7:7), the sojourn could have lasted no longer than 352 years.