The speed of the boat in still water

Question

Alvin paddles for five hours with a five kilometer/hour current to reach a campsite. The return trip against the same current took 10 hours. Find the speed of the boat in still water.

Answer 1

distance = rate x time

 

distance = (r + 5)*5

 

distance = (r-5)*10

 

5(r+5) = 10(r-5)

 

5r + 25 = 10r - 50

 

75 = 5r

 

r=15

 

The speed of the boat is 15 km/hr.

With the current, the boat goes 20 km/hr for 5 hours which is 100 km.

Against the current, the boat goes 10 km.hr for 10 hours which is 100 km.