SOLUTION: In 4 hours, Kerrie can go 15 miles upriver and come back. the speed of the current is 5 mph. what is the speed of the boat in still water?

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Question 810798: In 4 hours, Kerrie can go 15 miles upriver and come back. the speed of the current is 5 mph. what is the speed of the boat in still water?
Found 2 solutions by josgarithmetic, richwmiller:
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
Direction_________speed____________time_________________distance
upriver___________r-5______________(___)________________15
downriver_________r+5______________(___)________________15
Total________________________________4


The way Rate*Time=Distance works, know that Time=Distance/Rate:

Direction_________speed____________time_________________distance
upriver___________r-5______________15%2F%28r-5%29________________15
downriver_________r+5______________15%2F%28r%2B5%29________________15
Total________________________________4

Solve for r in highlight%2815%281%2F%28r-5%29%2B1%2F%28r%2B5%29%29=4%29

Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
a+b=4,
a*(r+5)=15,
15=b(r-5)
a = 1, b = 3, r = 10
10 mph in still water