A batch of parts was completed by group A alone in 36 hours. Now it is completed by the combination of A and B in 20 hours. Group A makes 5 more parts per hour than group B. How many parts are there in total?
一批零件由甲组独做36小时完成，现由甲、乙两组合做20小时完成，甲组每小时做的比乙组多5个．这批零件共有多少个．
<gadget id="calculator">1 / 36</gadget>
<output>1/36 = around 0.027778</output>

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

<gadget id="calculator">(1/20) - (1/36)</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/36) - (1/45)</gadget>
<output>1/180 = around 0.005556</output>

<gadget id="calculator">5 / (1/180)</gadget>
<output>900</output>

<result>900</result>