Where does “тридцатка” come from?

тридцатка (Russian) comes from Russian три́дцать, from Russian три, from Macedonian трие, from Proto-Slavic trьje, from Proto-Balto-Slavic tríjes, from Proto-Indo-European *tréyes.

тридцатка (Russian): sum of 30 rubles

Definitions

sum of 30 rubles

Ancestry of “тридцатка”, step by step

Step	Language	Word	Meaning
1	Russian	три́дцать	thirty (30)
2	Russian	три	three; second-person singular imperative...
3	Macedonian	трие	to rub
4	Proto-Slavic	trьje	three
5	Proto-Balto-Slavic	tríjes	three
6	Proto-Indo-European	*tréyes	—

Every word from Proto-Indo-European *tréyes →Every word from Proto-Balto-Slavic tríjes →Every word from Proto-Slavic trьje →