What is the speed of the river?

Question

A canoe can move at a speed of 2 mph in still water. The boat is paddled 4 miles downstream in a river in the same time it takes to go 1 mile upstream.

Answer 1

Time taken to go downstream = 4 / ( 2 + S) where S is the speed of the river

 

TIme taken to go upstream = 1 / ( 2 - S )

 

 

Since the time taken is the same in each case we can equate both of them

 

1 / ( 2 - S) = 4 / ( 2 + S )

 

 

2 + S = 8 - 4S

 

5 S = 6

 

S = 6 / 5

 

= 1.2 mph