Assertion: treadmill's speed | /r/HasProperty | 3 x 15/ 20 = 2.25 meters
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text: For example, if the belt length was 3 meters, and it took 20 seconds for it to do 15 revolutions, then the speed is (3 x 15) / 20 = 2.25 meters/second (or 8.1 km/hr or 5 mph).