There is a barrel of high-grade beverage, Xiaohua can drink it for 20 days alone, if he drinks it with Xiaofang, he can drink it for 12 days, if Xiaofang drinks it alone, how many days can he drink it.
有一桶高级饮料，小华一人可饮20天，若和小芳同饮则可用12天，若小芳独自一人饮，可用多少天．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) - (1/20)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>