SOLUTION: I need some help please. Juniors boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time it takes to go 9 miles upstream, the

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Question 161833: I need some help please.
Juniors boat will go 15 miles per hour in still water. If he can go 12 miles downstream in the same amount of time it takes to go 9 miles upstream, then what is the speed of the current?

Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
12/(15+c)=9/(15-c)
9(15+c)=12(15-c)
135+9c=180-12c
9c+12c=180-135
21c=45
c=45/21
c=2.143 mph is the current.
Proof:
12/(15+2.143)=9/(15-2.143)
12/17.143=9/12.854
.7~.7