



 
Vida, The key fact here is that rate = distance/time or said another way distance = time × rate. Suppose that the speed of the water current is w km/hr and the speed of the boat in still water is b km/hr. On the trip upstream the boat is pushing ahead at b km/hr but being pushed back by the stream at w km/hr and hence the net speed of the boat is (b  w) km/hr. At this speed it travels 20 km in 6 hours and distance = time × rate so
Write a similar equation for the trip downstream. Now you have two equation in b and w which you can solve. I hope this helps,  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 