There are 20 tons of coal, which can be transported by car A alone 4 times, and car B can be transported 5 times alone. How many times can the two vehicles be transported together? What is the column
有20吨煤，甲车4次可以单独运完，乙车5次可以单独运完．两车合运多少次可以运完？列式是多少
<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>

<result>20/9 = around 2.222222</result>