6. In a mathematics competition, the first round consists of 25 questions. According to the grading rules, each correct answer earns 4 points, and each incorrect or unanswered question deducts 1 point. If a score of no less than 60 points qualifies a student for the second round, then, the students who qualify for the second round must have answered at least. $\qquad$ questions correctly in the first round.
【Analysis】17 questions
If all answers are correct, the full score is $4 \times 25=100$ points, and for each wrong answer, $4+1=5$ points will be deducted; since the maximum deduction is $100-60=40$ points, which means a maximum of $40 \div 5=8$ questions can be answered incorrectly; therefore, at least $25-8=17$ questions need to be answered correctly.