It takes 20 days for A and B to process a batch of parts at the same time. It is known that the working efficiency ratio of A and B is 5:4. How many days does it take for B to process alone.
甲乙同时加工一批零件要20天，已知甲乙工作效率的比是5：4，乙单独加工要多少天．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(1/20) * (4/9)</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">1 / (1/45)</gadget>
<output>45</output>

<result>45</result>