Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
Thirty is regular. It follows the -ies Conversion rule.
Use plural verbs: "The thirties are ready" (not "is ready").
Yes. The plural thirties is standard across all English variants.
The word thirty follows the standard English pluralization rule. When forming the plural, thirty becomes thirties. This follows the -ies Conversion pattern, which is one of the most common plural rules in English.
Understanding why thirty becomes thirties helps with spelling and pronunciation. Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
When using thirties in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The thirties are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.