Genesis 11:12 "And Arphaxad lived five and thirty years, and begat Salah"
Luke 3:35-36 Which was the son of Saruch, which was the son of Ragau, which was the son of Phalec, which was the son of Heber, which was the son of Sala, 36 Which was the son of Cainan, which was the son of Arphaxad, which was the son of Sem, which was the son of Noe, which was the son of Lamech,
These two scriptures apparently contradict each other because Sala is clearly called the son of Arphaxad since Arphaxad begat him at the age of 35 in one passage, and in the other passage however, Sala is called the son of Cainan and grandson of Arphaxad. Both scriptures cannot both be true, there is no figure of speech involved, and the understanding of the words and expressions used is also clear. Since this apparent contradiction could not have been part of t he originally revealed Word of God, there remains then only one really plausible explanation for this difficulty: There must be somewhere in the text a mistake in the transmission of the text!
If we compare the geneologies in Genesis and in Luke from an overall perspective, we recognize that the difficulty arises in Luke 3 because of the addition of the person Cainan, and not because of the change of some other word. This Cainan does not figure anywhere else in the Bible, not in any of the other geneologies, not in the records with historical information about that particular time when he supposedly lived. All the other persons involved in these verses can be easily found in the various Biblical records and their existence can be determined without doubt. Cainan is the one great exception, and about him, there is no other mention in the Bible aside from the verse in Luke 3:36.
In some of the old manuscripts there are also differences as to the spelling of the word Cainan, in some other manuscripts Cainan is not even mentioned. It is quite sure therefore, that Luke 3:36 contains an interpolation, a rather dubious insertion done by a copyist which could be traced back to an addition in the Septuagint from the end of the 4th century AD.
Sala or Salah was definitely the son of Arphaxad, not the son of Cainan and therefore not Arphaxad's grandson.