SOLUTION: Trina's boat travels 20 km/h in still water. A river has a current that flows at a rate of 5 km/h. Trina travels in her boat downstream for 1 km and then returns to her starting po

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Question 1127041: Trina's boat travels 20 km/h in still water. A river has a current that flows at a rate of 5 km/h. Trina travels in her boat downstream for 1 km and then returns to her starting point. Her average rate, in km, is....?
I keep on getting 25km/h as the answer. I know it's wrong, but I don't know what I'm doing wrong. Thanks for helping.
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39617)   (Show Source): You can put this solution on YOUR website!
downstream,


upstream,


average speed for the whole round-trip,


-













,
Answer by ikleyn(52787)   (Show Source): You can put this solution on YOUR website!
.
Her speed downstream is 20 + 5 = 25 km/h.

She spent   of an hour traveling 1 kilometer downstream.



Her speed upstream is 20 - 5 = 15 km/h.

She spent   of an hour traveling 1 kilometer for the returning trip upstream.



In all, she spent   +  hours =  =  hours.



The average rate is the total distance, which is 1 + 1 = 2 kilometers, divided by the total time, which is   hours:


    the average rate =  =  =  = 18.75 kilometers per hour.    ANSWER

Solved.




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