A mountain road is 15 kilometers long. An athlete goes up the mountain at a speed of 3 kilometers per hour and then descends at a speed of 5 kilometers per hour. What is the average speed of the athlete for the round trip?
一条山路全长15千米，一名运动员以每小时3千米的速度上山，再以每小时5千米的速度下山，求这名运动员往返一趟的平均速度？
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">30 / 8</gadget>
<output>15/4 = around 3.75</output>

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