A car travels from A to B at an average of 45 kilometers per hour; when returning from B to A, it travels an average of 50 kilometers per hour. Find the average speed of the car traveling back and forth between places A and B.
一辆汽车从甲地开往乙地，平均每小时行驶45千米；从乙地返回甲地时，平均每小时行驶50千米．求这辆汽车在甲乙两地往返行驶的平均速度．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

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

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/45) + (1/50)</gadget>
<output>19/450 = around 0.042222</output>

<gadget id="calculator">2 / (19/450)</gadget>
<output>900/19 = around 47.368421</output>

<result>900/19 = around 47.368421</result>