ANSWER: There is no discrepancy, for the passages have not the same purpose. The latter text states the period of Israel's sojourn in Egypt beginning probably at Abraham's arrival in Haran a stranger. Israel was in Egypt alone but 250 years. Ex. 6:16-20, is a record only of the ages at death of Levi and his three sons, and is not chronological, because it does not give the age of the fathers at the birth of the son as in Gen. 11:10-27, where the period from Shem to Abraham is found by summing up all the generations from birth to birth.
— Steele's Answers pp. 206.