Answer:
Option A is correct, i.e. 3 mph.
Step-by-step explanation:
Tinh can row at a rate of 6 mph in still water.
Suppose the speed of the river current is X mph.
Then Upstream speed = (6-X) mph.
And Downstream speed = (6+X) mph.
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.
It means Distance upstream = Distance downstream.
Speed upstream x Time upstream = Speed downstream x Time downstream.
(6-x) * 2 = (6+x) * 40/60
12 - 2x = 4 + 2x/3
12 - 4 = 2x/3 + 2x
8 = 2x/3 + 6x/3 = 8x/3
x = 3 mph.
Hence, option A is correct, i.e. 3 mph.
Answer:
Option A (3)
Step-by-step explanation:
Given that Tinh can row at a rate of 6 mph in still water.
Also 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.
While upstream she travels against the stream but while downstream she travels along with the stream
Let x be the speed of boat in still water and y that of stream
Then since distance d is the same, time x speed =D
i.e. (x-y)120 = (x+y)40 after converting hours to minutes
80x=160y
x=2y
x=6 (given)
So y = 6/2=3 mph
