设甲乙两地全长为S 则有去时时间为S/40 则回时时间为S/50 2S÷(S/50+S/40) =2S÷(4S/200+5S/200) =2S÷9S/200 =400/9(km/分) ~师范附小李为您解答~ ~如果您满意请按下采纳,您的采纳是我前进的动力~