The radius of the wheel of a bicycle is 0.4 meters, how many meters does the wheel move forward in one revolution?
一辆自行车的车轮半径为0.4米，车轮往前滚动一周前进了多少米．
<gadget id="calculator">3.14 * 2 * 0.4</gadget>
<output>2.512</output>

<result>2.512</result>