Alex was confused. When he did a 20 mile round trip on the river it took him longer than it did to do a 20 mile round trip across the lake. He figured it closely using a GPS, and every time the results were the same.

His boat goes 10 miles an hour 1 and it takes him two hours to round trip 10 miles to his cabin across the lake and back. It takes him over two hours to go round trip to his fish camp which is also 10 miles downriver. The river current is 4 mph.

Round Trip Puzzle

Do the math for his round trip on the river in two segments up and down. Explain this to him.

Now that you understand this, how can he improve his gas mileage on the river?

Another Situation

Sam is on a swift river with a current averaging 6 mph. He has to make a round trip of 120 miles, and his boat is capable of doing 15 mph in still water. He checked all of this with the GPS.

How long would it take him to do a round trip? Why isn't the answer 8 hours?


Mark flies a plane to Palmer and back on a calm day, a flight of 250 miles. He uses 22 gallons of gas. His plane flies at 100 mph with floats.

He needs to go again, but it is blowing a 15 mph direct headwind. How much gas will hit take him to make the round trip?

Round Trip Puzzle

1 He used his GPS to compute his speed relative to the bank.

Formula D=RT

Round Trip Puzzle




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