"तू कितनी चाय पीता है?"

Translation: How much tea do you drink?

[DmitrijSil]

I spoke with my colleague native Hindi speaker and he recommended me to stick with "aap" for "you" by default even with children and unknown beggars and the like

[Sivapriya15]

You can use tum with your friends. I would not recommend using tu at all though.

[Mis-Jay]

Yep, definitely. "Aap" is much more formal than "tum" and "tu"

[silv1991]

I was surprised to see a sentence with तू so soon since it's only supposed to be used with people you're very close with.

[aaditsingh8]

The grammatical features of तू are easier to learn, considering the fact that they use the same verb endings as वह. This is why we thought तू would be easier to learn before तुम and आप! :)

[Baboo-Gustl]

Easier to learn compared to useful, I would prefer आप and तुम

[Sivapriya15]

Agree

[villajidiot]

Absolutely agree. It is best to teach आप first until that is what students use by default when they're not thinking about it. Then you can introduce तुम and explain when it is appropriate to use. Really तू should be left out of the course entirely at this level lest students unwittingly say very rude things.

[Alessandro510333]

why not कितना?

[MathWizard7]

Because चाय (Tea) is feminine.
Use कितना for masculine nouns.
Example: कितना पानी? How much water?
Use कितनी for feminine nouns.
Example: कितनी चाय? How much tea?
HTH

[Joannakingsly]

Is तुम accepted here?

[Brandzel]

Would this also be the way to ask "how many teas do you drink?" And if not, how would you ask that?