SOLUTION: The speed of a river is 4 mph. A boat travels 3 miles upstream (against the current) in the same amount of time it takes to travel 11 miles downstream (with the current). Find the

Question 930543: The speed of a river is 4 mph. A boat travels 3 miles upstream (against the current) in the same amount of time it takes to travel 11 miles downstream (with the current). Find the speed of the boat in still water (no current).
Answer by TimothyLamb(4379) (Show Source): You can put this solution on YOUR website!
x = speed of boat in still water
y = speed of current = 4 mph
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s = d/t
t = d/s
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upstream:
t = 3/(x - y)
t = 3/(x - 4)
---
downstream:
t = 11/(x + y)
t = 11/(x + 4)
---
equate times:
3/(x - 4) = 11/(x + 4)
3(x + 4) = 11(x - 4)
3x + 12 = 11x - 44
8x = 56
x = 56/8
x = 7
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answer:
x = speed of boat in still water = 7 mph
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