Xiaohong rides a bicycle from A to B, traveling 25 kilometers per hour when going there, and 15 kilometers per hour when returning. What is the average speed of Xiaohong going back and forth in kilometers per hour?
小红骑车从甲地到乙地，去的时候每小时行25千米，回来的时候每小时行15千米，小红来回一趟的平均速度是每小时多少千米．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/25) + (1/15)</gadget>
<output>8/75 = around 0.106667</output>

<gadget id="calculator">2 / (8/75)</gadget>
<output>75/4 = around 18.75</output>

<result>75/4 = around 18.75</result>