SOLUTION: A motorboat takes as long to go 12 miles downstream as to go 8 miles upstream. The river has a current of 3 miles per hour. What is the rate of the boat in still water?

Question 924344: A motorboat takes as long to go 12 miles downstream as to go 8 miles upstream. The river has a current of 3 miles per hour. What is the rate of the boat in still water?
Answer by TimothyLamb(4379) (Show Source): You can put this solution on YOUR website!
x = boat speed in still water
y = current speed = 3 mph
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down:
x + y = 12/t
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up:
x - y = 8/t
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x + y = 12/t
x - y = 8/t
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x = 12/t - y
x = 8/t + y
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x = 12/t - 3
x = 8/t + 3
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12/t - 3 = 8/t + 3
12/t - 8/t = 6
4/t = 6
t = 4/6
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x = 12/t - 3
x = 12/(4/6) - 3
x = 18 - 3
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answer:
x = 15 mph
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