Answer: 1/3?
Explanation:
The wording is a bit confusing. ". . . so 5 is what part of 9 is 3 . ." seems to be missing some portion of the sentence.
You ate 5/9 of the candies. There were 9 and you consumed 5. I don't know what you are asking in " . . what part of 9 is 3." 3 is 3/9, or 1/3.