A project can be completed by A in 12 days and by B in 15 days. A works for 4 days, B works for 3 days, how much of this project is completed?
一项工程，甲独做12天完成，乙独做15天完成．甲工作4天，乙工作3天，共完成这项工程的多少．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 4</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 3</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) + (1/5)</gadget>
<output>8/15 = around 0.533333</output>

<result>8/15 = around 0.533333</result>