Karen is paddling her canoe up a river against the current. On a still pond, Karen can paddle 10 miles per hour. The river flows in the opposite direction at 4 miles per hour. If the river is 12 miles long, how many hours will it take Karen to paddle up it?
First find Karen's net speed by subtracting the speed of the current: 10 mph - 4 mph = <<10-4=6>>6 mph
Then divide the length of the river by Karen's speed to find how long it takes her to paddle up it: 12 miles / 6 mph = <<12/6=2>>2 hours
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