17. (10 points) Xiao Hua walks along the route of the "Chunleibei" bus at a constant speed, encountering a "Chunleibei" bus head-on every 6 minutes, and being overtaken by a "Chunleibei" bus from behind every 12 minutes. How often does a "Chunleibei" bus depart? (Assume that "Chunleibei" buses depart from the terminal stations on both sides at regular intervals, travel at a constant speed, and do not stop at any station.)

Ask "Chunleibei" bus to depart every how many minutes?
【Answer】Solution: Suppose Xiaoming walked forward on the road for 12 (the least common multiple of 12 and 6) minutes, then immediately turned back and walked for another 12 minutes, returning to the starting point. During the first 12 minutes, he encountered $12 \div 6=2$ cars head-on, and during the next 12 minutes, $12 \div 12=1$ car caught up with him. Therefore, in the two 12-minute periods, he encountered a total of 3 cars heading in the same direction, so the interval between the departure of the cars is: $12 \times 2 \div (2+1)=8$ (minutes),

Answer: The "Chunlei Cup" cars are dispatched every 8 minutes.