SOLUTION: 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 th

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Question 831798: 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 by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
c = speed of the current.

_______________speed_______________time_____________distance
UP_____________6-c_________________2__________________d
DOWN___________6+c_________________2/3________________d

Same distance each way. Rate*Time gives the distance, and both expressions must be equal.
Forty minutes is the same as (2/3) hour. We can keep all in miles and hours.
%286-c%29%2A2=%286%2Bc%29%282%2F3%29
Simplify and solve for c.

2%2A3%286-c%29=2%286%2Bc%29
3%286-c%29=%286%2Bc%29
18-3c=c%2B6
18=c%2B3c%2B6
4c=12
RESULT: c=3 mph