Students go on an outing, travel 5 kilometers per hour when they go, and travel 3 kilometers per hour when they come back, what is the average speed of their round trip in kilometers per hour?
同学们去郊游，去时每小时行5千米，回来时每小时行3千米，他们往返的平均速度是多少千米/时．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/5) + (1/3)</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">2 / (8/15)</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>