A and B work together to make a batch of machine parts, and the task can be completed in 20 days. It is known that the ratio of work efficiency between A and B is 5:4, how many days will it take for A to make this batch of parts alone?
甲乙两人合做一批机器零件，20天可以完成任务．已知甲、乙两人工作效率的比是5：4，甲单独做这批零件要几天完成？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">(1/20) * (5/9)</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">1 / (1/36)</gadget>
<output>36</output>

<result>36</result>