A motor boat can travel 30 km upstream and 28 km downstream in 7 hours.I can travel 21 km upstream and return in 5 hours. Find the speed of the boat in still water and the speed of the stream.(We're supposed to find the speed of boat downstream here too ... so..)
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motor boat speed for upstream=Vu =30/7 =4.28kmph
& speed of boat in Downstream=Vd =28/7=4
Let speed at still water be v
Speed of stream=Vs=Vd-v
=>Vs=4-v
Also speed of stream =Vs=v-Vu=v-4.28
=>4-v=v-4.28
=>2v=4+4.28=8.28
=>v=4.14kmph(velocity of boat in still water)
Speed of stream=Vd-v=4.28-4.14=0.34kmph
& speed of boat in Downstream=Vd =28/7=4
Let speed at still water be v
Speed of stream=Vs=Vd-v
=>Vs=4-v
Also speed of stream =Vs=v-Vu=v-4.28
=>4-v=v-4.28
=>2v=4+4.28=8.28
=>v=4.14kmph(velocity of boat in still water)
Speed of stream=Vd-v=4.28-4.14=0.34kmph
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