Xiao Chen drove a helicopter from Guangzhou to Shanghai to watch the World Expo. He was very excited when he went there. He drove very fast at a speed of 150 km/h. When he returned, he was very tired and drove very slowly at a speed of only 100 km/h. : What is the average speed of Xiaohu going back and forth between Guangzhou and Shanghai?
小陈从广州开直升飞机去上海看世博，去时很兴奋，开的很快，速度为150千米/时，回时很累，开的很慢，速度只有100千米/时，问：小胡往返广州和上海的平均速度是多少．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 150</gadget>
<output>1/150 = around 0.006667</output>

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

<gadget id="calculator">(1/150) + (1/100)</gadget>
<output>1/60 = around 0.016667</output>

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

<result>120</result>