<PRE><B>Question 821105</B>
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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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