Learn Swedish: Ett tiotal trasiga kundvagnar lämnades kvar. - Around ten broken shopping carts were left behind.

Adding the neuter suffix -tal to a number creates a collective noun that expresses an approximation. While tio means exactly ten, ett tiotal means a group of about ten or around ten.

Since ett tiotal is a singular ett-word, why is the adjective trasiga in the plural form?

The adjective agrees with the actual items being counted, which is the plural noun kundvagnar (shopping carts). Even though ett tiotal is grammatically singular, the phrase as a whole represents a plural quantity, so we use the plural adjective ending -a.

Why isn't there a preposition like av (of) between the quantity and the items, like in the English a group of ten?

In Swedish, collective numerical nouns ending in -tal are placed directly in front of the adjectives and nouns they modify, completely without a preposition. You treat ett tiotal structurally just like a regular number.

What role does the -s play at the end of the verb lämnades?

It forms the s-passive in the past tense. If we used the active past tense lämnade, it would mean the carts actively left something else. By using lämnades, the sentence correctly shows that the carts were the objects being left by an unnamed person.