The circular runway is 400 meters long. A and B start from the same place clockwise at the same time. A runs 110 meters per minute, and B runs 90 meters per minute. How many minutes later the two meet.
环形跑道长400米，甲、乙两人同时从同一地点顺时针出发，甲每分钟跑110米，乙每分钟跑90米，多少分钟后两人相遇．
<gadget id="calculator">110 - 90</gadget>
<output>20</output>

<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<result>20</result>