Xiao Min and her mother take a walk by the lake. It takes Xiao Min 40 minutes to walk around the lake, and it takes 50 minutes for her mother to walk around the lake. If two people start from the same place at the same time and walk towards each other, how many minutes later will they meet?
小敏与妈妈一起在湖边散步，小敏走一圈要40分钟，妈妈走一圈要50分钟．若两人同时同地出发，相背而行，多少分钟后相遇？
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/40) + (1/50)</gadget>
<output>9/200 = around 0.045</output>

<gadget id="calculator">1 / (9/200)</gadget>
<output>200/9 = around 22.222222</output>

<result>200/9 = around 22.222222</result>