Rashi continues and mentions a possible alternate explanation: The Jews left "mechamushim" meaning one out of every five Jews were taken out of Egypt, and the other four-fifths died during the plague of darkness.

Both of these explanations are wonderful, but there is a problem. Usually, when Rashi brings a second explanation, the additional one is in some way related to the first explanation. However, in this case, the two ideas seem to be totally unrelated.

If we take a look at the Aramaic translation/commentary of Yonatan ben Uziel, he states that "chamushim" means that every Jew came out with five children. Now, if we look at another Aramaic translation, this time the commentary of the Targum Yerushalmi, it explains that the Jews left armed with good deeds.

Now we can understand the connection between Rashis two seemingly unrelated explanations of the word chamushim, the first that the Jews left Egypt armed, and the second that one-fifth of the Jews were taken out of Egypt while the remaining ones died during the plague of darkness. The Jews went up from Egypt armed with good deeds. These good deeds consisted of the surviving Jews taking in the wives and children of the four-fifths who perished during the ninth plague of darkness. Those surviving Jews were armed with the merit of the acts of kindness they did in taking care of their deceased brothers families as if they were their own.

Good Shabbos!