A boat has a 10-gallon gasoline tank and travels at 20mph with a fuel consumption of 16mi/gallon when operated at full throttle in still water. The boat is moving upstream into a 5mph current. How far upstream can the boat travel and return on 10 gallons of gasoline if it is operated at full throttle during the entire trip ?
I think Stolyar is correct, but I solved it in a different way.
At 20 miles per hour and 16 miles/gallon, that is equal to 20/16 = 5/4 gallons per hour. This rate of consumption is constant throughout the problem.
At 5/4 gallons per hour, the boat will run for 10/(5/4) = 8 hours.
Hence 15 * T1 = 25 * T2 (distances up and down stream are the same)
and T1 + T2 = 8 (total time is 8 hours).
Solve for either T1 or T2 then plug back in to get D = 75 miles.
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