一位教师为启迪智力、发展能力,对学生讲了如下例题:〔例1〕甲、乙两人骑自行车分别从相距90公里的 A、B 两地同时相向而行。甲每小时行17公里,乙每小时行13公里。经几小时相遇?若相遇后两人继续前进,甲到 B、乙到 A 后均立即往回走,问何时第二次相遇?继续下去,何时第三次相遇?第四次相遇?……乃至第几次相遇?解:90÷(17+13)=3(小时),即出发后3小时,两人相遇。由第一次相遇至第二次相遇,二人行程和为180公里,180÷(17+13)=6(小时)。以后各次相遇亦 A teacher teaches students the following examples for enlightening intelligence and developing their abilities: [Example 1] A and B ride their bicycles from opposite sides of A and B respectively 90 km apart. A line of 17 kilometers per hour, B line 13 kilometers per hour. After a few hours to meet? If two people continue to move forward after the encounter, A to B, B to A immediately after all go back and ask when the second encounter? Continue, when the third encounter? Fourth encounter? ... and even the first encounter? Solution: 90 ÷ (17 + 13) = 3 (hours), that is, 3 hours after departure, the two met. From the first encounter to the second encounter, the two trips and 180 km, 180 ÷ (17 + 13) = 6 (hours). After each encounter also