Naughty participated in the 400-meter race in the school sports meeting. He ran 4 back and forth on the runway, how long is this runway?
淘气参加了校运动会的400米跑比赛．他在跑道上跑了4个来回，这条跑道有多长？
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">400 / 8</gadget>
<output>50</output>

<result>50</result>