A car travels from A to B at a speed of 72 kilometers, and immediately returns to A at a speed of 48 kilometers per hour. Find the average speed of the car per hour.
汽车以72千米的速度从甲地到乙地，到达后立即以每小时48千米的速度返回甲地，求该车的平均速度是每小时多少．
<gadget id="calculator">1 / 72</gadget>
<output>1/72 = around 0.013889</output>

<gadget id="calculator">1 / 48</gadget>
<output>1/48 = around 0.020833</output>

<gadget id="calculator">(1/72) + (1/48)</gadget>
<output>5/144 = around 0.034722</output>

<gadget id="calculator">2 / (5/144)</gadget>
<output>288/5 = around 57.6</output>

<result>288/5 = around 57.6</result>