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 of

Algebra ->  Polynomials-and-rational-expressions -> 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 of      Log On


   

Question 329308: 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 of the current?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Rate*Time=Distance
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Let W be the speed of the current,
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.
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1.%2815%2BW%29%2At=12<-- with the current
2.%2815-W%29%2At=9<--- against the current
From eq. 1,
15%2BW=12%2Ft
From eq. 2,
15-W=9%2Ft
Add those two results,
15%2BW%2B15-W=21%2Ft
30=21%2Ft
t=21%2F30
Then from eq. 1,
15%2BW=12%2830%2F21%29=120%2F7
W=120%2F7-105%2F7
W=15%2F7mph