A project is completed in 20 days by A alone, 30 days by B alone, and 3 days after A and B work together, what fraction of the project is left?
一项工程，甲独做20天完成，乙独做30天完成，甲乙合做3天后，还剩下这项工程的几分之几？
<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">(1/12) * 3</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<result>3/4 = around 0.75</result>