Wang Fei went to the city library to borrow books. When he went, he walked 5 kilometers per hour; when he returned from the original road, he traveled 20 kilometers per hour by car. What is his average speed back and forth?
王飞到市图书馆借书，他去时步行每小时行5千米；从原路返回时乘车每小时行20千米．他来回的平均速度是多少？
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/5) + (1/20)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / (1/4)</gadget>
<output>8</output>

<result>8</result>