A man travels 12 km. down a river and back in 4.5 hours. If his rate in still water is 6 km/hr, what is the rate of the river current?
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time = distance /rate
4.5 = 12/(6+v) + 12/(6-v)
3 = 8/(6+v) + 8/(6-v)
3(6+v)(6-v) = 8(6+v) + 8(6-v)
108-3v^2 = 96
3v^2 = 12
v^2 = 4
v = 2 km/hr
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4.5 = 12/(6+v) + 12/(6-v)
3 = 8/(6+v) + 8/(6-v)
3(6+v)(6-v) = 8(6+v) + 8(6-v)
108-3v^2 = 96
3v^2 = 12
v^2 = 4
v = 2 km/hr
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