Why not "tu peut"?
"tu peux" - with an "x"
But why the X?
Conjugation of verb 'pouvoir' :
je peux, tu peux, il/elle/on peut, nous pouvons, vous pouvez, ils/elles peuvent.
verb2verbe.com is a great resource on verb conjugations. Pouvoir is an irregular verb.
Duo translation, as shown, "Vous pouvez manger seul?" Should it not be "seuls" since they are using the plural form of "you"? I was marked wrong and will report it, but maybe I'm missing something?
I don't get it... why is the last 'e' optional?
Have you not noticed that when you say "you" you can be talking to a man or a woman? In French it is the same, so because French adjectives agree with the gender, you can have "seul" if "you" is a man or "seule" if "you" is a woman.
est-ce que vous pouvez manger seuls...why is this wrong?
It is not wrong, you can consider that this is a plural "vous" and that this group consists of men or a mix of men and women. In that case, "vous pouvez manger seuls" is correct.
If all women: "vous pouvez manger seules".
And why my answer "Pouvez-vous manger seuls?" is wrong?
It shouldn't be wrong.
I type "vous pouvez mangent seul". why mangent is not correct?
"mangent" is the conjugation of verb manger (inf.) matching pronouns ils/elles (they).
In this construction, you have to use the infinitive form: vous pouvez MANGER...
why not vous pouvez mangez seul?
"pouvoir" is one of those verbs that are constructed with the infinitive form (modal verb)
thank you so much for your prompt reply
Tu peux manger seul? Would also be correct, yes?
Or would it be better. Peux tu manger seul ?
Yes, it is correct and now all possible translations are accepted.