It takes 20 hours for the master to process 1000 parts alone, and 25 hours for the apprentice to process alone. How many hours will it take for the two to work together?
加工1000个零件，师傅单独加工要20小时，徒弟单独加工要25小时，两人合作要多少小时完成？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(1/20) + (1/25)</gadget>
<output>9/100 = around 0.09</output>

<gadget id="calculator">1 / (9/100)</gadget>
<output>100/9 = around 11.111111</output>

<result>100/9 = around 11.111111</result>