The distance between A and B is 600 kilometers. The average speed of a car in the first half of the journey is 100 kilometers per hour, and the average speed in the second half of the journey is 60 kilometers per hour. What is the average speed of this car in kilometers per hour?
甲乙两地相距600千米，一辆汽车前一半路程的平均速度是每小时100千米，后一半路程的平均速度是每小时60千米，这辆汽车的平均速度是每小时多少千米．
<gadget id="calculator">600 / 2</gadget>
<output>300</output>

<gadget id="calculator">300 / 100</gadget>
<output>3</output>

<gadget id="calculator">300 / 60</gadget>
<output>5</output>

<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">600 / 8</gadget>
<output>75</output>

<result>75</result>