What is the speed of the boat in still water?

Question

A boat travels 20 kilometers upstream in the same time that it would take the same boat to travel 30 kilometers downstream. If the rate of the stream is 5 kilometers per hour, find the speed of the boat in still water.

Answer 1

Let x = speed of boat in still water

 

Speed downstream = x+5

Speed upstream = x-5

 

Distance = (Rate)(Time), so Time = Distance/Rate

 

Time upstream = Time downstream

 

So, 20/(x-5) = 30/(x+5)

 

Cross multiply to get 20(x+5) = 30(x-5)

 

                              20x+100 = 30x-150

 

                                      10x = 250

 

                                         x = 25 km/hr