The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Ew. Fifty? We'll be old and gross.
The Big Bang Theory Season 8, Episode 24

- How many guards does my father have?
- Here in King's Landing? Fifty.
Game of Thrones Season 1, Episode 5

Dredging's almost
at FIFTY percent.
Westworld Season 2, Episode 5

Seventeen FIFTY? We'll make it 1750,
for, like, you know, interest.
Breaking Bad Season 2, Episode 4

Thirty, forty, FIFTY coffees a day.
Money Heist Season 3, Episode 7