Trigonometry
posted by Laura .
A water wheel has a radius of 15 ft. A river passing through the water wheel turns the wheel at 11 revolutions per minute(rpm). What is the speed of the river in miles per hour?

what's the circumference of the wheel? 30pi
So, 30pi ft flows by 11 times per minute
That makes a river speed of 30pi*11 ft/min
Now convert that to mi/hr