It takes 10 days for A to complete the processing of a batch of parts, and 15 days for B to complete it alone. A works for 2 days first, and then the two work together. How many days will it take to process this batch of parts?
加工一批零件，甲单独完成需10天，乙单独完成需15天．甲先做2天后两人再合做，加工完这批零件一共需要多少天？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</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">(4/5) / (1/6)</gadget>
<output>24/5 = around 4.8</output>

<gadget id="calculator">(24/5) + 2</gadget>
<output>34/5 = around 6.8</output>

<result>34/5 = around 6.8</result>