There is a batch of books that A can bind every day (1/40), and B can bind every day (5/6). How many days can A and B work together to finish binding?
有一批书，甲每天可以装订(1/40)，乙20天可以装订(5/6)，甲、乙两人合做几天可以装订完？
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(5/6) / 20</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/40) + (1/24)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / (1/15)</gadget>
<output>15</output>

<result>15</result>