It takes 10 days for A to dig a 611-meter canal alone, and 15 days for B to do it alone. Now, how many days will it take for A and B to do the whole project (2/3)?
挖一条611米的水渠，甲单独做要10天完成，乙单独做要15天完成，现在甲乙合做全部工程的(2/3)，需要几天？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

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

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

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

<result>4</result>