A boat goes downstream for 3 hours. Then it turns and goes upstream for 5 hours. Then it turns again, goes 10 miles downstream until it arrives where it initially started. What is the speed of the boat if the speed of the stream is 3 mph? How long does the boat need for the third part upstream?
What would happen if the speed of the stream would be 6 mph? Can the speed of the boat and the time the boat needs for the last part be expressed in terms of the speed of the stream?
Erich Prisner, June 2004