There is a distance between A and B. It is downhill from A to B. The speed when going downhill is 100 kilometers per hour, and the speed when returning is 60 kilometers per hour. Then the average speed of the round trip is 1 hour How many kilometers.
A、B两地之间有一段路程，从A到B是下坡，下坡时的速度为每小时100千米，返回时的速度为每小时60千米，那么往返的平均速度是每小时多少千米．
<gadget id="calculator">1 * 2</gadget>
<output>2</output>

<gadget id="calculator">1 / 100</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/100) + (1/60)</gadget>
<output>2/75 = around 0.026667</output>

<gadget id="calculator">2 / (2/75)</gadget>
<output>75</output>

<result>75</result>