A and B set off from the east city to the west city at the same time. A travels 30 kilometers per hour, and B travels 50 kilometers per hour. After traveling for 10 hours, B arrives at the west city and returns immediately. He meets A on the way. How many hours did it take to meet.
甲乙两人同时从东城向西城出发，甲每小时行30千米，乙每小时行50千米，行了10小时后乙到达西城，又马上返回，在途中与甲相遇，两人从出发到相遇用了多少小时．
<gadget id="calculator">30 + 50</gadget>
<output>80</output>

<gadget id="calculator">2 / 80</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">50 * 10 * (1/40)</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>