Dad took Xiaoyong to climb the mountain on weekends. The distance from the bottom of the mountain to the top of the mountain was 7.2 kilometers. Their speed up the mountain was 2.4 kilometers per hour, and their speed down the mountain was 3.6 kilometers per hour. What is the average speed of going up and down the mountain?
双休日爸爸带小勇去登山，从山下到山顶全程7.2千米，他们上山的速度是2.4千米/小时，下山的速度是3.6千米/小时，上、下山的平均速度是多少？
<gadget id="calculator">7.2 + 7.2</gadget>
<output>14.4</output>

<gadget id="calculator">7.2 / 2.4</gadget>
<output>3</output>

<gadget id="calculator">7.2 / 3.6</gadget>
<output>2</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">14.4 / 5</gadget>
<output>2.88</output>

<result>2.88</result>