Learn Romanian: O serie de greșeli au distrus proiectul. - A series of mistakes have destroyed the project.

This is an example of logical agreement, the focus of this lesson. When a singular collective noun (like o serie, o mulțime, or un grup) is followed by de + a plural noun (like greșeli), Romanian often puts the verb in the plural to match the logical doers of the action—the mistakes themselves.

Would it be incorrect to use the singular verb a distrus here to strictly match o serie?

No, it wouldn't be incorrect. Grammatical agreement (matching the singular o serie with the singular a distrus) is also correct and sometimes preferred in formal writing. However, logical agreement (au distrus) is completely acceptable and often sounds much more natural in everyday communication.

What is the singular form of greșeli, and why does the spelling change?

The singular is o greșeală (a mistake). It is a feminine noun. Notice the vowel alternation: the ea diphthong in the singular root changes to an e when forming the plural greșeli. This is a common pattern for feminine nouns ending in -eală.

What dictates the suffix -ul on the word proiectul?