A project can be completed in 5 days by A alone, and 8 days by B alone, how much of the whole project can be completed by two people working together in 2 days?
一项工程，甲单独做需要5天完成，乙单独做需要8天完成，现两人合做2天，能完成全工程的多少．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/5) + (1/8)</gadget>
<output>13/40 = around 0.325</output>

<gadget id="calculator">2 * (13/40)</gadget>
<output>13/20 = around 0.65</output>

<result>13/20 = around 0.65</result>