Breakdown of Oitenta por cento dos inquiridos responderam ao questionário.
do
of the / from the (do, da, dos, das)
ao
to the / at the (m.sg; f.sg à, m.pl aos, f.pl às)
oitenta
eighty
responder
to reply
Questions & Answers about Oitenta por cento dos inquiridos responderam ao questionário.
Why is responderam in the plural here?
With percentages, the verb usually agrees with the noun that follows the percentage. Here, that noun is inquiridos (respondents), which is plural, so the verb takes the plural form responderam. If the noun had been a collective singular, like in oitenta por cento do grupo, the verb would be singular.
Since oitenta is plural, what happens if the percentage is exactly one percent?
If the sentence started with um por cento dos inquiridos, you would have a choice. You could use the singular to agree with the number um, or the plural to agree with the noun inquiridos. Both are grammatically correct in European Portuguese, but agreeing with the noun is generally the most natural choice.
The word inquiridos looks like a verb. How is it being used here?
It is the past participle of the verb inquirir (to inquire or to question). Here it acts as a noun meaning the people who were questioned, or the respondents. Using past participles as nouns is very common in Portuguese to describe groups of people based on an action done to them.
Why do we say responderam ao questionário instead of just responderam o questionário?