Xiaohong and her father go climbing on Sunday. When going up the mountain, they walk 20 meters per minute. After reaching the top of the mountain, they return along the same road and walk 30 meters per minute. What is their average speed for going up and down the mountain?
小红和爸爸周日去爬山，上山时每分钟行20米，到达山顶后沿原路返回，每分钟行30米，他们上山和下山的平均速度是多少？
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">2 / (1/12)</gadget>
<output>24</output>

<result>24</result>