Learn Arabic (Modern Standard): وصل عشرون جنديا إلى المعسكر.

In Arabic, when a sentence starts with a verb, the verb stays in the singular form even if the subject following it is plural. Since عشرون (twenty) acts as a masculine subject here, we use the 3rd person masculine singular verb وصل. If the subject had been placed before the verb, the verb would have needed a plural form.

Why is the number twenty written as عشرون here instead of عشرين?

Decade numbers (20, 30, 40, etc.) change their endings based on their grammatical role in the sentence, similar to regular sound masculine plurals. Because twenty is the subject doing the arriving, it is in the nominative case, which takes the ـون ending. If it had been the object of the sentence or followed a preposition, it would be عشرين.

The English translation says soldiers (plural), so why does the Arabic use the singular word جنديا?

In Arabic, the rules for counting nouns change depending on the number category. For numbers from 11 to 99, the counted noun must be singular and take the accusative case, meaning it typically ends with an -an sound written with an alif. That is why we use the singular جنديا instead of the plural جنود.