8 Arrange fifteen students numbered $1,2,3, \ldots, 15$ in a circle facing inward, in numerical order. The first time, the student numbered 1 turns around. The second time, the students numbered 2 and 3 turn around. The third time, the students numbered $4,5,6$ turn around, .... The 15th time, all students turn around. When the 12th turn is completed, how many students are still facing outward?
【Answer】12
【Analysis】Key points: Reverse reasoning, parity
If all 15 rounds are completed, there will be a total of $1+2+3+\cdots+15=120$ turns, with each student turning $120 \div 15=8$ times.
In the 15th round, all students turn once. Since the 15th round did not occur, each student turns 7 times.
In the 14th round, students with numbers $15, 14, 13, \ldots, 3, 2$ turn.
In the 13th round, students with numbers $1, 15, 14, 13, \ldots, 5, 4$ turn.
In these two rounds, students numbered $1, 2, 3$ turn once, and students numbered $4, 5, \ldots, 15$ turn twice. Therefore, after 12 rounds, students numbered $1, 2, 3$ turn 6 times and face inward; students numbered $4, 5, \ldots, 15$ turn 5 times and face outward. At this point, 12 students are facing outward.