SOLUTION: a boat takes 2 hours to go 30 km downstream and 3 hours to go the same distance upstream. finds its speed in still water.

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Question 404881: a boat takes 2 hours to go 30 km downstream and 3 hours to go the same distance upstream. finds its speed in still water.
Answer by Tatiana_Stebko(1539) About Me  (Show Source):
You can put this solution on YOUR website!
If the boat speed is x kmh, river speed is y kmh, then when boat go downsteram it speed is %28x%2By%29, upstream speed is %28x-y%29
a boat takes 2 hours to go 30 km downstream, so downstream speed is 30%2F2=15 kmh, so %28x%2By%29=15
a boat takes 3 hours to go 30 km upstream, so upstream speed is 30%2F3=10kmh
so %28x-y%29=10
Equations system
x%2By=15
x-y=10Add the first equation to the second
.
2x=25
x=25%2F2
x=12.5 kmh is the boat speed
The river speed is 12.5%2By=15 y=15-12.5 y=2.5kmh
Answer The boat speed is 12.5 kmh