бист

Рақами хонаи мо бист аст.
Our house number is twenty.
Дар соати бист дақиқа кам нӯҳ аз хона мебароям.
At twenty minutes to nine I leave the house.

Bonus:
When combining thousands, hundreds, tens and digits you use у (or ю), and.
бисту як: twenty-one
саду бист: one hundred and twenty
дусаду бисту панҷ: two hundred and twenty-five

To change a cardinal number to an ordinal number add the suffix ум (or юм).
бистум: twentieth

When writing ordinal numbers often the number is written instead of the word, and then hyphenated with the ending, for example:
20-уми май: 20th of May

When a noun comes after a number, the noun does not take the plural ending.
гулҳо: flowers
бист гул: twenty flowers