I don't think it's silly, it's only a sentence without a context. You guessed the context, so it can be understood.
Those kinds of sentences make us use our brain. Grammatically this sentence is not wrong, and in the meaning, it can be said in a dialogue.
In French, the meaning is the same than "Combien en cuisines-tu?"
But French uses the particle "en", that is not known in English, except if you translate it with "it", "of it". But it would seem very redundant to say "How many do you cook of this" in a normal dialogue.
How many things are you cooking. It can be cakes or anything what can be cooked.
It's implied. The person who said this sentence already knows it, as it was stated in a previous sentence, who can see (but we cannot), it's part of a dialogue:
-I bake chocolate cakes!
-Oh! How many are you cooking?
-I bake sesame breads!
-Oh! How many are you cooking?
Oh, sorry--you're right; I was looking at another part of the thread and got confused about what the original Duo sentence was.
My apologies, Vitruvi !
Since it's not uncommon for "five of them," "some of us," and similar locutions to be expressed as quīnque ex eīs and quīdam ē nōbīs (which are literally "5 out of them," "some out of us"), you might think of quot ē vōbīs coquitis , if you want "How many of you are cooking?" (rather than "How many are you cooking?")
Quello che dici è vero e ben trovato, but it belongs to other level. In order to avoid ambiguous sentences and answers you can simply include a direct object. Of course, many people would consider inappropriate to write things like Quot psittacos ebrios coquitis?, but how about crustulas?
Sure; Quot crustula coquitis for "How many cookies are you cooking?", is great. One can imagine an exchange such as: Quid coquitis? (WHAT are you cooking?); Crustula coquimus . (We're cooking cookies.); Quot coquitis ? (How many are you cooking?)
Assuming neuter plural crustula , that is.
If it can't be implied, how come we guessed what they mean?
Implied means you can guess it (even when it's not said).
How come it can be perfectly grammatical in a dialogue? If it's possible to be implied in a dialogue, it's correct in English, de facto. Not everything can be implied in a dialogue.
So, 2 points here. It is implied and perfectly grammatical.
In linguistics, it's called "implied complement of transitive verbs", and I'm sorry, but it's perfectly valid. (yes, it's disturbing, and it's probably the reason of your complaint, but being disturbing is another thing)
Other examples of implied complement (not a transitive)
Yesterday I couldn't decide whether or not to go to the beach"
"What did you do?"
The Cambridge grammar book gives other examples:
She's the director of the company.
Without a complement (implied):
She's the director.
I'm certain it's genuine.
I haven't seen her since the war.
I haven't seen her since.
(here a transitive preposition used with an implied complement)
All the complements given in the 2nd sentences, are implied. When something is obviously implied, we know that the previous sentence or the fact to see directly the scene explain the exact meaning of the implied thing.
= >There's no need to have it in a dialogue, if you see the scene, the sentence is also perfectly normal.