Question

A kayaker can paddle 12 mi in 2 h moving with the river current. Paddling at the same pace, the trip back against takes 4 h. Assume that the river current is constant. Find what the kayakers speed would be in still water.

Answer 1

Downstream DATA:
distance = 12 miles 
time = 2 hours 
rate = 12/2 = 6 mph
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Upstream DATA:
distance = 12 miles 
time = 4 hrs 
rate = 12/4 = 3 mph
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Equations:
Downstream: b + c = 6
Upstream::: b - c = 3
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Add to get:
2b = 9
b = 4.5 mph (speed of the boat in still water.)
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Solve for "c":
b + c = 6
4.5 + c = 6
c = 1.5 mph (speed of the current)
The answer is 1.5 mph