

Автобус придёт через тридцать минут.
The bus will come in thirty minutes.
Моему брату уже тридцать лет.
My brother is already thirty years old.
В апреле тридцать дней.
April has thirty days.
"тридцать" is in the lesson "Big numbers" (Level 4), along with 11 other useful words. LinDuo has 180 topic lessons like this one, 2,380 words in total. Every word has an illustration, a transcription and pronunciation in a female and a male voice. Just 10–15 minutes a day is enough to learn them all. Free, and works offline.