Dad took Xiaoyong to climb the mountain on weekends. The whole journey from the bottom of the mountain to the top of the mountain was 7.2 kilometers. It took them 3 hours to go up the mountain and 2 hours to go down the mountain. What is their average speed up and down the mountain in kilometers per hour?
双休日爸爸带小勇去登山，从山底到山顶全程7.2千米，他们上山用了3小时，下山用了2小时．他们上、下山的平均速度是每小时多少千米？
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">7.2 * (2/5)</gadget>
<output>2.88</output>

<result>2.88</result>