A project can be completed in 15 days by A alone, and 10 days by B alone. If A completes (1/3) of the project first, and the rest is done jointly by A and B, it will take several days Finish?
一项工程，甲单独做要15天完成，乙单独做要10天完成，如果甲先做了这项工程的(1/3)，剩下的由甲、乙合做，还要几天才能完成？
<gadget id="calculator">1 / 3</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">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">(1/15) + (1/10)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(2/3) / (1/6)</gadget>
<output>4</output>

<result>4</result>