Xiaoqiang's home is 120 kilometers away from his grandma's house. Xiaoqiang rides a bicycle at 15 kilometers per hour and returns at 10 kilometers per hour. What is the average speed of Xiaoqiang's round trip in kilometers per hour?
小强家距奶奶家有120千米，小强骑自行车去每小时15千米，回来时每小时10千米，小强往返的平均速度是每小时多少千米．
<gadget id="calculator">120 / 15</gadget>
<output>8</output>

<gadget id="calculator">120 / 10</gadget>
<output>12</output>

<gadget id="calculator">8 + 12</gadget>
<output>20</output>

<gadget id="calculator">2 / 20</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">120 * (1/10)</gadget>
<output>12</output>

<result>12</result>