If A alone takes 8 days to complete a project, and B alone takes 10 days to complete it, how many days can the two cooperate to complete it?
一项工程，甲单独做要8天完成，乙单独做要10天完成，两人合作多少天能够完成．
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/8) + (1/10)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">1 / (9/40)</gadget>
<output>40/9 = around 4.444444</output>

<result>40/9 = around 4.444444</result>