A piece of work, it takes 20 hours for A to complete independently, and 30 hours for B to complete alone. If they finish this work together, how much more will A do than B after the completion of this work.
一件工作，A独立完成要20小时，B独立完成要30小时，如果他们共同完成这项工作，完成后A比B多做了这项工作的多少．
<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>

<gadget id="calculator">(1/20) * 12</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(1/30) * 12</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>