A car drives from place A to place B, traveling 80 kilometers per hour, returning immediately after arriving at the destination, and traveling 100 kilometers per hour when returning. What is the average speed of this car going back and forth between A and B?
一辆汽车从甲地开往乙地，每小时行80千米，到达目的地后立即返回，返回时每小时行100千米．这辆汽车往返甲、乙两地的平均速度是多少千米？
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 80</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">1 / 100</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">(1/80) + (1/100)</gadget>
<output>9/400 = around 0.0225</output>

<gadget id="calculator">2 / (9/400)</gadget>
<output>800/9 = around 88.888889</output>

<result>800/9 = around 88.888889</result>