на прошлых

at the previous; in the last (used with plural nouns)

→ на
phrase Very common #2,044
at the previous; in the last (used with plural nouns) На прошлых is the prepositional plural form of на прошлый and is used before plural nouns, such as на прошлых выборах (“in the last elections”) or на прошлых встречах (“at previous meetings”).
RU: На прошлых выборах она впервые голосовала.
EN: She voted for the first time in the last election.

Это правда, что ты был на прошлых выходных в Бостоне?

Is it true that you were in Boston last weekend?

На прошлых выходных Том был со своей семьёй.

Tom was with his family last weekend.