A person rides a motorcycle to and from A and B, travels 30 kilometers per hour when going, and travels 45 kilometers per hour when returning, what is the average speed of this person going back and forth?
某人骑摩托车往返于甲、乙两地，去时每小时行30千米，回来时每小时行45千米，此人往返的平均速度是多少．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 45</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/30) + (1/45)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">2 / (1/18)</gadget>
<output>36</output>

<result>36</result>