標題: Help:F.3 Maths [打印本頁] 作者: tommy26 時間: 20/8/2009 03:02 PM 標題: Help:F.3 Maths ON a downstream trip, aman rows a boat for a distance of 66km in three hours; on an upstream trip, he rows the same distance in six hours. Find the speed of the current and the speed of the boat in still water rowed by the man作者: inthomaspy 時間: 20/8/2009 04:21 PM 本帖最後由 inthomaspy 於 20/8/2009 04:59 PM 編輯
Speed of the boat downstream = 66km / 3hr = 22 km/h Speed of the boat upstream = 66km / 6hr = 11 km/h
Speed of the boat downstream = Speed of the boat rowed by the man in still water+Speed of water current Speed of the boat upstream = Speed of the boat rowed by the man in still water-Speed of water current (As the motion of water current is against the rowing action by the man)
Hence, let speed of water current be x km/h and that of the boat rowed by the man in still water be y km/h In the downstream journey, x + y = 22 ...(1) In the upstream journey, y - x = 11 ...(2)