SOLUTION: The speed of a river current is 4 mph. If a boat travels 30 miles downstream in the same time that it takes to travel 20 miles upstream, find the speed of the boat in still water.

Question 820972: The speed of a river current is 4 mph. If a boat travels 30 miles downstream in the same time that it takes to travel 20 miles upstream, find the speed of the boat in still water.

Answer by TimothyLamb(4379) (Show Source): You can put this solution on YOUR website!
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s = d / t
t = d / s
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down:
T = 30/(s + 4)
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up:
T = 20/(s - 4)
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30/(s + 4) = 20/(s - 4)
30(s - 4) = 20(s + 4)
30s - 120 = 20s + 80
10s = 200
s = 20
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answer:
boat speed in still water = 20 mph
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