Acts 7:14 states that "Joseph sent word and invited Jacob his father and all his relatives to come to him, seventy-five persons in all." This seems to contradict Deut. 10:22, Ex. 1:5; and Gen. 46:27 which all say it was 70 persons. What accounts for this difference?
Acts 7:14 is part of a speech which Luke records. The speech is given by Stephen, a Greek Jew who no doubt would have read the Septuagint. The Septuagint (along with the Dead Sea Scrolls) varies from the Masoretic Text in both Genesis 46:27 and Exodus 1:5 and reads instead "75 people." It's likely Stephen was quoting this tradition.
Gen 46:27 indicates that 66 biological descendants of Jacob had traveled to Egypt. That is, when Joseph and his two sons are not counted from the genealogy (along with Er and Onan, who had died previously in Canaan), the number is 66 people according to the Masoretic Text. Thus 66 biological descendants of Jacob traveled to Egypt. This number did not include the wives of the sons of Jacob (Gen 46:26).
However, Gen 46:27 indicates that 70 people traveled to Egypt. In this regard, the additional four people appear to have been -
Finally, the Septuagint (LXX) indicates 75 people, as noted in Acts 7:14 of the Christian New Testament. That is, the Genesis passage in the LXX reads as follows:
Thus the LXX takes the perspective: 66 + 9 = 75. That is, the 66 biological descendants of Jacob plus the nine children of Joseph (as noted in the LXX) would comprise the people "who came into Egypt." In this regard, Jacob and his three wives are excluded from the count. From this perspective, Jewish tradition, provides yet additional (and alternative) information to consider this problem.
As apparent in Acts 7:14, Joseph desired that Jacob and all his relatives would live and remain with him in Egypt. So, if the 66 biological relatives plus Jacob and his three wives comprised the 70, who were the other five people, whom Joseph wished to live and remain with him from the apparent perspective of Jewish tradition (which assumes that Joseph only had two sons)?
The additional five would appear to be -
The latter two had died in Joseph's absence--that is, they died after Joseph was sold into slavery in Egypt, and so Joseph may have learned from Judah that they were born to him (Judah) during the 22 year hiatus (that is, Joseph's absence), but not that they had died. As regards Jochebed, according to the Talmud, Jochebed (Levi's daughter) had been conceived, but yet unborn when she arrived in Egypt in the womb of her pregnant mother. Thus she constituted a living person albeit unborn. According to the translation of the Babylonian Talmud by Neusner (2011), we read the following in b. Baba Batra 8:4, II.4.D -
In other words, if Joseph's two sons (Manassah and Ephraim) are included with Jochebed, Er, and Onan as part of the "in all" (NASB translation of Acts 7:14), then the LXX number of 75 persons would comprise "Jacob and all his relatives"--that is, Jacob's direct relations, whom Joseph had desired to live and remain with him in Egypt from the apparent perspective of Jewish tradition (which assumes that Joseph only had two sons).
In summary, the Masoretic Text and the LXX (with additional information supplied from Jewish oral tradition in the Talmud) appear to be aspects of the same issue, but viewed at from different angles.
Neusner, Jacob (2011). The Babylonian Talmud: A Translation and Commentary (Vol. 15). Peabody, MA: Hendrickson Publishers, 361.