WAS SHELAH THE SON, OR GRANDSON, OF ARPHAXAD?

Genesis 11:12 And Arphaxad lived five and thirty years, and begat Salah: (KJV) 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, 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, (KJV)

Luke was going from a copy of the OT that had been translated into Greek. For some reason, the Greek version of the OT gave the genealogy presented in Luke.  The most likely explanation is that the Greek OT was correct, and the Hebrew one had skipped over Cainan.  Skipping a generation in a Hebrew genealogy is not unheard of, and neither does it invalidate the genealogy.  Many genealogies in the Bible skip over generations.  So the Genesis 11 passage is not incorrect, since Arphaxad probably did live for 35 years, and he did ultimately begat Salah, though through his son Cainan.  Not a contradiction.