Two teams, A and B, make a batch of model airplanes, which can be completed in 8 days. If group A does it alone for 20 days, how many days does group B do it alone?
甲乙两个小组合做一批航模，8天可完成．如果甲组单独做20天完成，乙组单独做几天完成？
<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>