The car is driving on a straight road. The speed of the first half of the journey from A to B is 40 kilometers per hour, and the speed of the second half is 60 kilometers per hour. The time speed is 60 kilometers per hour, find the average speed difference of the car going back and forth.
汽车在平直的公路上行驶，从A到B前一半路程速度为每小时40千米，后一半路程速度为每小时60千米，回来时前一半时间速度为每小时40千米，后一半时间速度为每小时60千米，求汽车往回的平均速度差．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 40</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">(1/2) / 60</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">(1/80) + (1/120)</gadget>
<output>1/48 = around 0.020833</output>

<gadget id="calculator">1 / (1/48)</gadget>
<output>48</output>

<gadget id="calculator">50 - 48</gadget>
<output>2</output>

<result>2</result>