SOLUTION: John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the

Question 58777This question is from textbook Elementry and Intermediate algebra
: John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the speed of the water currents? This question is from textbook Elementry and Intermediate algebra

Found 2 solutions by checkley71, stanbon:
Answer by checkley71(8403) (Show Source): You can put this solution on YOUR website!
12/(15+X)=9/(15-X)
9(15+X)=12(15-X)
135+9X=180-12X
9X+12X=180-135
21X=45
X=45/21
X=2.14 MPH IS THE SPEED OF THE WATER
PROOF
12/(15+2.14)=9/(15-2.14)
12/17.14=9/12.86
.7=.7
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the speed of the water currents?
----------------
Let speed of the current be "c".
---------------
Downstream DATA:
distance = 12 mi. ; Rate = 15+c mph ; time=d/r=12/(15+c) hrs.
---------------
Upstream DATA:
distance =9mi ; rate = 15-c ; time = d/r= 9/(15-c)
--------------
EQUATION:
time down = time up
12/(15+c) = 9/(15-c)
12(15-c)=9(15+c)
180-12c=135+9c
45=21c
current speed =15/7= 2.15 mph
Cheers,
Stan H.

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