Learn Icelandic: Fjórir strákar eru þreyttir.

In Icelandic, the numbers 1, 2, 3, and 4 change to match the gender of the noun they are counting! The default counting number for four is the neuter form fjögur. But since strákar (boys) is a masculine noun, we must use the masculine form fjórir.

How do we form the plural for "boys" here?

The singular form is strákur (a boy). For many masculine words that end in -ur, you drop the -ur and add -ar to make them plural, giving us strákar (boys).

Why does the word for tired (þreyttir) end in -ir?

Adjectives have to match the noun they describe in gender and number. The base word for "tired" is þreyttur. Because we are talking about multiple boys (masculine plural), it becomes þreyttir. You might notice that fjórir and þreyttir rhyme—this -ir ending is a very common pattern for masculine plural words!

What form of the verb "to be" is eru?

Eru is the form of the verb vera (to be) used for "they are" and "you (plural) are". Since "four boys" represents "they", we use eru.