need help with my question

Question

a paddle boat can move at a speed of 20 km/h in still water. The boat is paddled 14 km downstream in a river in the same time it takes to go 7 km upstream. What is the speed of the river?

Answer 1

Hi Aaron,

 

The formula is distance/rate = time.

 

Let X = the speed of the river

 

So the boat speed upstream = 20 - X . . . the boat goes slower because it's fighting against the current

 

and the boat speed downstream is 20 + x . . .the boat goes faster because it flowing with the current.

 

Times are the same upstream and downstream.

 

upstream distance = 7 and downstream distance = 14

 

So 14/((20+X) = 7/(20 -X)

 

Cross multiply--> 14(20-X) = 7(20+X)

 

280 - 14X = 140 + 7X

 

140 = 21X

 

X = 6.666666666 km/h

 

Dan