Question

Tinh can row at a rate of 6 mph in still water. It takes her 2 hours to row upstream from a dock to a park. She then rows back to the dock, and it only takes 40 minutes. What is the speed of the river current?

Answer 1

Answer: The speed of the river current = 3mph

Step-by-step explanation:

Let x be the speed of the river current.  

Given: The speed of Tinh in still water = 6 mph

Let d be the distance from dock to park.

Now, speed in upstream = 6-x

Time taken in upstream = 2 hours

Distance covered upstream =$d=speed*time=2(6-x)$....(1)

Speed in downstream = 6+x

Time taken in downstream = 40 minutes =$=\frac{40}{60}$hour= 2/3 hour

Distance covered downstream =$d=speed*time=\frac{2}{3}(6+x)$.....(1)

From (1) and (2), we have

$2(6-x)=\frac{2}{3}(6+x)\\\Rightarrow\ (6-x)=\frac{1}{3}(6+x)\\\Rightarrow\ 3(6-x)=6+x\\\Rightarrow\ 18-3x=6+x\\\Rightarrow\ x+3x=18-6\\\Rightarrow\ 4x=12\\\Rightarrow x=3$

Hence, The speed of the river current = 3mph

 

Answer 2

I just got the right answer and its 3