題目:
A boat travels60 km upstream in120 minutes, and returns downstream in72 minutes. Suppose the speed of the stream is x km/h ,and the speed of the boat in still water is y km/h.
Q(1): Express, in terms of x and y, the seed of the boat travelling upstream.
Answer: (y-x) km/h
Q(2): Express, in terms of x and y, the seed of the boat travelling downstream.
Answer: (y+x) km/h
更新1:
回白色彗星: 我想問下點解水流速同船速係相反就要將船速減番水流速呢?? 唔該晒....... (恕我愚蠢= =")
