Chabad.org — English translation + Rashi
Torah Temimah (Pesachim 79a): when Israel is half tahor and half tamei, the status is treated as a majority for the purpose of not deferring the whole community.
English: It was stated: If Israel were half tahor and half tamei — Rav said: half-and-half is like a majority. And Rav Kahana said: half-and-half is not like a majority.
Half-and-half rule — the verse’s individual language keeps the community from being pushed to the second month.
Even a perfect split does not dissolve the communal character of the first Pesach.