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:
Gen 46:27 (NETS)
27 And the sons of Ioseph who were born to him in the land of Egypt were nine persons. All the persons of Iakob’s house who came into Egypt were seventy-five.
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 -
- Manasssah (son of Joseph)
- Ephraim (son of Joseph)
- Jochebed (daughter of Levi born in Egypt - Nu 26:59)
- Er (died in Canaan)
- Onan (died in Canaan)
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 -
He said to him, “I had a valuable pearl in my hands, and you want to take it away from me! This is what R. Hama bar Hanina said, ‘This refers to Jochebed, who was conceived on the way [down to Egypt] and was born between the walls of Egypt: ‘… who was born to Levi in Egypt’ (Num. 26:59), meaning, her birth was in Egypt but not her conception.”
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.
As to the question of 66 vs. 70 going down to Egypt:
Genesis 46:26 states: "All the souls coming to Egypt with Jacob, those descended from him, excluding the wives of Jacob's sons, all the souls were sixty six."
The above excludes both Jacob and the women, as it's said "with Jacob" (thus excluding).
Joseph and his 2 sons were already in Egypt. Therefore, once Jacob and his descendants arrived, there were a total of 70 (The 66 plus Jacob, Joseph, and Joseph's 2 sons). As verse 46:27 states: "all the souls who came to Egypt".
Verse 46 says "coming to Egypt". Verse 47 says "who came to Egypt". Therefore verse 47 includes those already there, whereas verse 46 hadn't included those already there.
The 66 persons in Gen. 46:26, 1. Joseph, 2. Manasseh, 3. Ephraim, 4. Er and
5. Onan were excluded but Jacob was included (70-5+1=66).
In Gen. 46:27, it is exact in citing 70 went "with Jacob" which means that Jacob was excluded in the counting and the wives (Jacob's and 12 sons).
In the book of Acts 7:14 it is counted 75. How can it be? Stephen possibly counted 1. Leah, 2. Bilhah, 3. Zilphah, 4. Dinah (daughter of Jacob) and 5. Serah (daughter of Asher - Gen. 46:17). Rachel was not included because she was already dead (Gen. 35:19).
The answer may lay in Acts 7:14 where Joseph invites his father Israel and all his relatives ( meaning Joseph and all his grandchildren) . We allready know that the remaining wife (Lea) and two other mothers of his children were not numbered among the seventy, as were not numbered the wives of his sons . In Genesis 46:6 is mentioned something where I think the answer is hidden. In the children counts is mentioned Dina, daughter that Lea have him, and Sera, daughter of Asher. But....in 46:6-7 is mentioned : they came in Egypt, Jacob and all his seed with him. His sons and the sons of his sons with him, his daughters and the daughters of his sons, and all his seeds he brought with him in Egypt.
This was the invitation. You notice the plural in his daughters ? So there was one or two more daughters born to Jacob in Kanaän except Dina . You notice the plural in daughters of his sons? So there was one or more granddaughters born to Jacob except Sera. Together 5, and that answers the question of the difference.
First references here's an opportunity to see what I saw when attempting to answer this question on my own with a little help.
Summary of Genesis 46:9-14.
From Reuben (Hanoch, Phallu, Hezron, & Carmi). 
From Simeon (Jemuel, Jamin, Ohad, Jachin, Zohar, & Shaul) 
From Levi (Gershon, Kohath, & Merari) 
From Judah (Er, Onan, Shelah, Pharez, Zerah, Hezron, & Hamul) 
From Issachar (Tola, Phuvah, Job, & Shimron) 
From Zebulun (Sered, and Elon, and Jahleel) 
Gen 46:15 These were the sons of Leah, whom she bore to Jacob in Padan-aram, and his daughter Dinah. All the souls of his sons and his daughters were [thirty three].
Gen 46:18 These were the sons of Zilpah, whom Laban gave to his daughter Leah; and she bore these to Jacob, [sixteen souls].
Gen 46:22 These were the sons of Rachel which were born to Jacob; all the souls were [fourteen].
Gen 46:25 These were the sons of Bilhah whom Laban gave to his daughter Rachel; and she bore these to Jacob, all the souls were [seven].
Gen 46:27 And the sons of Joseph which were born to him in Egypt, two souls. All the souls belonging to the house of Jacob coming into Egypt were [seventy].
This is what I noticed. In the count we have 33, 16, 14, & 7. Adding these numbers gives us 70, obviously. The number 75 comes from the 5 names in bold. I included a summary of verses 9-14. This way we can all together note that Dinah isn't included in the original count for 33.
One may want to disregard Rachel as she died on the way to Bethlehem (Gen. 48:7). However, if this were the case I would also believe that Er & Onan who also died in the land of Canaan would also be disregarded. (Gen. 46:12)
Therefore it is my humble opinion that the number 75 came from including all the names in this passage.