"What is the quantity?"
Translation:Quelle est la quantité ?
Doesn't work. "Combien" is only for countable things. How many cars are there? Combien il y a-t-il de voitures? How much milk do you want? Quelle quantité de lait voulez-vous?
In English the word quantity can be used for both countable and uncountable nouns and as such can be synonymous with the word number for countable nouns.
Output in economics is the "quantity of goods or services produced in a given time period, by a firm, industry, or country", whether consumed or used for further production.
The sentence What is the quantity ? could be a question relating to the statement:
Consumer demand determines the quantity of washing powders that this supermarket provides.
Therefore in this context the question What is the quantity ? is equivalent to: What is the number ?
In French (since we're talking about this specific language here), "quantité" is, as far as I know, only used for uncountable things. Perhaps you could find counter-examples, but it'd wouldn't be rigorous French.
So if you've got the question "Quelle est la quantité", the question is necessarily about something uncountable.
To re-use your examples:
"Quelle quantité de lessive l'entreprise a-t-elle produite cette année?" "What quantity of washing powder did the company produce this year?" => 10 tonnes (you can't answer by 1, 2, 3...)
If you want to ask the question about cars, or any countable thing, you have to use "combien" (how many cars did the company produce). "Quelle quantité de voitures" is grammatically wrong)
Firstly the french word combien can be used as an adverb of quantity meaning how many or how much and can apply to both countable and uncountable nouns. So I don't think your statement Combien is only for countable things is correct
combien d’argent avez-vous? - How much money do you have ?
Combien d'eau ? - How much water?
avez-vous besoin combien de temps? - How much time do you need?
Combien de quantité d'eau employons-nous réellement?
Secondly, the original query related to whether the English sentence What is the quantity could be translated into French using combien. Note that the English sentence is ambiguous as it can refer to a countable or uncountable noun.
Thirdly, I don't think your statement "quantité" is, as far as I know, only used for uncountable things is correct.
quantité d'indications laissent supposer qu'il est mort - A number of indications lead one to think he is dead.
Quantité de gens ne se sont jamais posé la question. (from Larousse dictionary)
The noun quantité without an article can be used with plural nouns (both countable and uncountable) to indicate a number of them
Fourthly, you misused my example relating to washing powder. My statement was about washing powders (different brands) and not washing powder being used as an uncountable noun. The letter s at the end of washing powder is important in my example.
I'm really pleased by the exchange we're having here, because it makes me think on my own language, on things I "take for granted" without thinking about it.
I think your summary is quite good, to the best of my knowledge. But as for the French language, there're always exceptions and oddities xD
About "sommeil" = This is again an interesting and relevant example.
"How much sleep do you need?" = I think "sommeil" is grammatically countable. Naturally, I'd translate it as "De combien d'heures de sommeil avez-vous besoin?" and the answer would be "8 hours" or "10 hours", so something countable by a unit of time.
"Quel est le sommeil dont vous avez besoin?" = doesn't make much sense as if there were different types of sleep and you needed one in particular among them.
"De combien de sommeil avez-vous besoin?" (don't forget the "de") = Completely understandable even though I think mentionning the "hours" in your question would be more rigorous.
So you could basically say that when you're refering to sleep, you're implicitly refering to time, and so sleep works like time in grammar.
Be aware that if you go to France, you'll probably hear people mixing all these up quite often ^^
Hope it helps
I'll try to explain my point a bit more clearly. Note that I'm just a native speaker trying to help Duolingo learners and I do not prentend to be a scholar of linguistics in anyway.
About "combien" for countable things :
Combien d’argent avez-vous? = I think money could be seen as grammatically countable, but I'm not 100% sure. De combien de temps avez-vous besoin? = same thing. Those two examples are perhaps grammatical oddities because I agree that it's not self-evident that "money" should be more countable than, for example, "milk".
Combien d'eau ? = grammatically wrong (I know some people would say "Combien de farine mets-tu dans le gateau?" but I'm pretty sure it's an "abus de langage", i.e. a mistake). Combien de quantité d'eau employons-nous réellement? = grammatically wrong
About quantity: my point wasn't about the word "quantité", but about the question "Quelle est la quantité de + noun? " (I reckon my phrasing wasn't cristal clear here). If you use this question, you can only be talking about uncountable things. I'm taking your examples again (which I find very thought provoking):
"Quantité d'indications laissent supposer qu'il est mort." = Sure indications are countable. If you want to ask a question about this, you'd say "Combien d'indications avez-vous?" and not "Quelle quantité d'indications..." (because it's countable). I don't know why, that's just how it is. Perhaps the explanation would be that "quantité de ..." is a fixed idiom.
"Quantité de gens ne se sont jamais posé la question." = This sentence is completely fine too. And to build a question about this you'd have to use "combien".
About washing powders: If I understand what you mean, your original example was something like "What quantity of (different) washing powderS does the company produce?". I would translate that as "Combien de différentes sortes de lessives l'entreprise produit-elle?" because "types or brands of washing powders" is countable. However "Quelle quantité de lessive l'entreprise produit-elle? L'entreprise produit dix tonnes de lessives." would work as an uncountable noun.
"Consumer demand determines the quantity of (different) washing powders that this supermarket provides." = "La demande des consommateurs détermine le nombre de lessives que le supermarché fournit" => "Combien de lessives (différentes) le supermarché fournit-il? Le supermarché fournit 10 lessives différentes."
I hope I'm clear enough.
Thanks for your detailed reply
So to sum up:
in French if you want to say:
how much of something uncountable you use: quelle est la quantité + uncountable noun
how many of something countable you use: combien de + countable noun
but there are exceptions such as * combien de temps
if I want to translate the sentence: How much sleep do you need, then it is:
Quel est le sommeil dont vous avez besoin
Combien de sommeil avez-vous besoin
because the word sommeil in this context an uncountable noun