On a 400-meter circular runway, two brothers run clockwise from the same starting point at the same time, and they meet every 10 minutes. If the speed of the two people remains the same, and they still start from the original starting point at the same time, and the elder brother runs counterclockwise instead, and the two meet each other every 5 minutes, how many minutes will it take for the slower of the two to run a lap?
在一条400米的环形跑道上，兄弟两人同时从同一个起点按顺时针方向跑步，两人每隔10分钟相遇一次．若两个人的速度不变，还是从原出发点同时出发，哥哥改为按逆时针方向跑，结果两人每隔5分钟相遇一次，那么，两人中较慢的跑一圈要多少分钟．
<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<result>20</result>