There are a bunch of goods, which need to be transported 20 times by large trucks, and 30 times by small trucks. If large and small trucks are used together, how many times will it take to finish the shipment?
有一堆货物，用大卡车运，要运20次；用小卡车运，要运30次．若用大、小卡车一起运，需要多少次才能运完？
<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">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>