A project alone needs 15 days to complete. If A works alone for 5 days first, and B does the rest of the project alone, it can be completed in 8 days. If A works alone for 10 days first, and B alone does the rest, how many days can it be completed?
一项工程，甲单独做需要15天完成．若甲先单独做5天，余下的工程由乙单独做，8天可以完成．若甲先单独做10天，余下的工程由乙单独做，则多少天可以完成．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 10</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/15) * 5</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) / 8</gadget>
<output>1/12 = around 0.083333</output>

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

<result>4</result>