A project can be completed in 10 hours by A alone, 8 hours by B alone, and after 4 hours of cooperation between A and B, how much of the project is left to be completed.
一件工程，甲独做要10小时完，乙独做要8小时完，甲、乙合作4小时后，还剩这件工程的多少没完成．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

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

<gadget id="calculator">(9/40) * 4</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>