SOLUTION: The speed of a stream is 3 mph. A boat travels 4 miles upstream in the same time it takes it to travel 10 miles downstream. What is the speed of the boat in still water?

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Question 208299: The speed of a stream is 3 mph. A boat travels 4 miles upstream in the same time it takes it to travel 10 miles downstream.
What is the speed of the boat in still water?

Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
D=RT
T=D/R
T=4/(R-3)
T=10/(R+3)
4/(R-3)=10/(R+3)
10(R-3)=4(R+3)
10R-30=4R+12
10R-4R=12+30
6R=42
R=42/6
R=7 MPH IS THE SPEED OF THE BOAT.
PROOF:
4/(7-4)=10/(7+3)
4/4=10/10
1=1