posted by on .

A motorboat can travel upsteam on a river at 18km/h and downsteam at 30km/h. How far upstream can the boat travel if it leaves at 8:00am and must return by noon?

18t=30•(4-t)
18t =120 -30t
48t=120
t=120/48 =2.5
18•2.5=45 km
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