Learn Icelandic: Fólkið selur marga notaða hluti á markaðnum. - The people sell many used things at the market.

In Icelandic, fólk is a grammatically singular neuter noun. Even though it refers to multiple individuals, you treat it like a single collective group (similar to "the crowd" or "the team" in English). That is why it takes the 3rd person singular verb selur rather than the plural selja.

Wait, aren't we learning about weak adjectives? Why are marga and notaða strong here?

Adjectives generally only use their weak forms when they follow a definite article, a demonstrative pronoun (like "this" or "that"), or a possessive. Because there is no "the" or "these" in front of "many used things" here, the adjectives stay strong. If you wanted to say "these used ones" (dropping the noun like in this lesson), you would use the weak form: þessa notuðu.

Why is the word for "things" hluti instead of hlutir?

Hlutur (thing) is a masculine noun. In this sentence, it is the direct object receiving the action of the verb selur, so it must be in the accusative case. The accusative plural of hlutur is hluti (dropping the -r). The adjectives marga and notaða are also in the masculine accusative plural to match.

Why is "at the market" (á markaðnum) in the dative case?