Xiaohong and her father go climbing on Sunday. When they go up the mountain, they walk 30 meters per minute. After reaching the top of the mountain, they return along the same road. When they go down the mountain, they walk 50 meters per minute. What is their average climbing speed?
小红和爸爸周日去爬山，上山时每分钟行30米，到达山顶后沿原路返回，下山时每分钟行50米，他们爬山的平均速度是多少？
<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 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/30) + (1/50)</gadget>
<output>4/75 = around 0.053333</output>

<gadget id="calculator">2 / (4/75)</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>