SOLUTION: Junior's boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed fo th

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Question 197838: Junior's boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed fo the current?
I am not even sure where to start here... I'm freaking out!
Answer by solver91311(24713) About Me  (Show Source):
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Going downstream, the speed of the current adds to the speed of the boat in still water, so if r represents the unknown speed of the current, the speed downstream is . Likewise, going upstream, the speed of the current subtracts from the speed in still water, so:

Using the downstream trip is described by:



And the upstream trip:



Since the problem says both trips take the same amount of time, set the two fractions equal to each other and solve the proportion by cross-multiplying.

John