Huahua and Beibei set off from the same place by the circular pool at the same time in opposite directions. 9 minutes, how many minutes does it take for Huahua and Beibei to meet each other?
华华、贝贝二人由圆形池边的同一地方，按相反方向同时出发，在途中相遇后继续前进，华华从相遇地点到出发地需4分钟，贝贝从相遇地点到出发地点需9分钟，华华、贝贝二人相遇需多少分钟．
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/9) + (1/4)</gadget>
<output>13/36 = around 0.361111</output>

<gadget id="calculator">1 / (13/36)</gadget>
<output>36/13 = around 2.769231</output>

<result>36/13 = around 2.769231</result>