If A and B cooperate to complete a project, it takes 8 days to complete it, and B alone takes 20 days. How many days does it take A to do it alone?
一项工程，甲、乙合作需8天完成，乙单独做需20天，甲独做需多少天？
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

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

<gadget id="calculator">(1/8) - (1/20)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">1 / (3/40)</gadget>
<output>40/3 = around 13.333333</output>

<result>40/3 = around 13.333333</result>