A circular runway is 400 meters long, A travels 100 meters per minute, and B travels 50 meters per minute. A and B set off in the same direction at the same time, how long will it take for them to meet again?
一条环行跑道长400米，甲每分钟行100米，乙每分钟行50米．甲、乙两人同时同地同方向出发，问多长时间后他们再相遇？
<gadget id="calculator">100 - 50</gadget>
<output>50</output>

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

<result>8</result>