It takes Xiao Ming 10 hours to go from A to B, and it takes 8 hours to return from B to A. What is Xiao Ming's average round trip speed?
小明从甲地到乙地去时用10小时，从乙地返回甲地要8小时，小明往返的平均速度是多少？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/10) + (1/8)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">2 / (9/40)</gadget>
<output>80/9 = around 8.888889</output>

<result>80/9 = around 8.888889</result>