Learn Polish: Trzy czwarte ludzi myśli, że stres wzrasta. - Three quarters of people think that stress is increasing.

In Polish, fractions are built using a cardinal number (like trzy) and a feminine ordinal number (like czwarte). This is because the underlying word for 'part' (część) is feminine. So, trzy czwarte literally means 'three fourth (parts)'. Since trzy is plural, the ordinal number takes the non-masculine-personal plural form czwarte.

Why is the verb myśli (thinks) in the singular when the subject is multiple people?

When a fraction (like trzy czwarte) or a quantity word is the subject of a sentence, the verb must be in the third-person singular. Even though it represents many people, Polish grammar treats the fraction itself as a single grammatical block. If this were in the past tense, it would take the neuter singular form (trzy czwarte ludzi myślało).

Why is ludzi in the genitive case here?

After fractions and expressions of quantity, the noun that follows must be in the genitive case. Just like in English you say 'three quarters of people', Polish uses the genitive plural ludzi to express that 'of' relationship.

Could I use rośnie instead of wzrasta for 'is increasing'?

Yes, they are very similar! Wzrasta (from wzrastać) is often used for abstract concepts like stress, prices, or numbers. Rośnie (from rosnąć) is also perfectly fine here, but it is a bit more general and is the primary word used for physical growth, like plants or children growing up.