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Yes.
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(less fewer)
You’re on a correct path if your use of the word “less” refers to the percentage of questions that you answer, but not completely correct (see below). I read it and understood it as you referring to the number of questions you answer, hence the word “fewer” would be correct.
Grammatically speaking, you can’t have “less percentage”. You can, however, have “less of a percentage” or “a lower percentage. Depending on your intent, the angle from which to view the passage dictates which words are correct, and the perception or interpretation of the reader(s) in understanding your meaning is another angle.
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Probably less." [...than 25% of the questions posted would be inferred].
That’s still “fewer”.
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Hey, I’ve seen that episode!
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