In the Torah we are told that 600,000 Jews left Egypt (Shmos 12:37). It also says that the Jewish people left Egypt “Chamushim” (Shmos 13:18). Rashi explains that the word “Chamushim” is based on the Hebrew word for five and it means that only 1/5th of the Jews were alive after the plague of darkness (חוֹשֶך). He explains that the others died because they were wicked and did not want to leave Egypt. (Rashi on Shemos 10:22) How many Jews died during the plague of darkness?
600,000 = 1/5 the total
4 x 600,000 = 2,400,000 Jews died during the plague