Breakdown of Какое количество? У нас около пятнадцати штук.
мы
we
какой
which/what kind of (m, sister forms: какая, какое)
у
at, by
пятнадцать
fifteen
Questions & Answers about Какое количество? У нас около пятнадцати штук.
Why is the number written as пятнадцати instead of the dictionary form пятнадцать?
The preposition около (about/around) requires the word following it to be in the Genitive case. Numbers from 5 to 20 end in a soft sign (-ь) and decline just like feminine nouns ending in -ь (such as тетрадь). To form the Genitive case, you replace the -ь with -и, giving us пятнадцати.
Since около puts the number in the Genitive case, does it also change the case of штук?
The number itself dictates the case of the noun. When a number is in an oblique case like the Genitive (as пятнадцати is here), the noun that follows it must match that case. Because we are talking about multiple pieces, we use the Genitive plural. The dictionary form is штука (piece), and its Genitive plural is штук. (Note: Even if the number were in the Nominative case, numbers 5 and above still require the Genitive plural for the noun!)
Why use штук here instead of just saying "about fifteen"?
In Russian, it's highly common to use the word штука (piece, item, thing) when counting inanimate objects, similar to saying "fifteen of them" or "fifteen items" in English. You will hear it constantly in everyday Russian speech when the specific object being counted is already understood from context.
Why does the question use Какое instead of Какой?