"These hints and tips came out of a 12,000 person research study."
If so, can we use the word (people) instead of (person)?
Best English can we use the word (people) instead of (person)? No. 'person' is correct.
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Best Englishcan we use the word (people) instead of (person)?
No. 'person' is correct. You might hyphenate that compound adjective, though: 12,000-person.
CJ