Final answer:
The tradition behind "LXX" (70) serving as the symbol for the Septuagint is the number of translators involved in the translation.
Step-by-step explanation:
The tradition behind "LXX" (70) serving as the symbol for the Septuagint is the number of translators involved in the translation. The Septuagint is a Greek translation of the Hebrew Bible, and according to legend, it was translated by seventy (LXX) Jewish scholars. The number 70 became associated with the Septuagint as a symbol of its origins and authority.