Learn Polish: Zaledwie jedna czwarta ankietowanych ma czas wolny. - Merely one quarter of the respondents have free time.

Fractions in Polish use feminine forms because they implicitly agree with the feminine noun część (part). You are essentially saying jedna czwarta (część), meaning one fourth part.

Since there are many respondents, why is the verb ma in the singular form?

The verb agrees with the main grammatical subject of the sentence. Here, the subject is the singular fraction jedna czwarta (one quarter), not the plural ankietowanych. Therefore, we use the singular verb ma.

What case is ankietowanych and why?

It is in the genitive plural. After fractions and quantities, Polish uses the genitive case to express the English word of. Here, it means a quarter of the surveyed people. The word itself is a passive participle (ankietowany - surveyed) acting as a noun.

Why is the adjective placed after the noun in czas wolny instead of before it?

Adjectives typically go before the noun, but when they create a specific category or fixed phrase (like free time or foreign language), they usually go after it. Czas wolny is a standard set phrase in Polish.