A tourist group took a boat to visit the Mingchuan scenic spot 15 kilometers away from the station. It traveled 25 kilometers per hour when going there, and 15 kilometers per hour when returning by the original road. What is the average round trip speed?
某旅游团乘船向离驻地15千米的名川胜地观光，去时每小时行25千米，原路返回时每小时行15千米．往返的平均速度是多少？
<gadget id="calculator">15 / 25</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">(3/5) + 1</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">2 / (8/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">15 * (5/4)</gadget>
<output>75/4 = around 18.75</output>

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