It takes 4 days for A to process a batch of parts, and 5 days for B to do it alone. If two people work together, A will make 20 more parts than B when the work is completed. How many parts are there in total?
加工一批零件，甲单独做要4天，乙单独做要5天，如果两人合做，完工时甲比乙多做了20个零件，这批零件共有多少个？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) + (1/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 / (9/20)</gadget>
<output>20/9 = around 2.222222</output>

<gadget id="calculator">(1/4) * (20/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">(1/5) * (20/9)</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(5/9) - (4/9)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">20 / (1/9)</gadget>
<output>180</output>

<result>180</result>