project can be completed by team A alone in 15 days, and team B can complete it in 5 days less than team A. After team A works for a few days, team B joins in and it takes another 2 days to complete. How many days does team A work first?
一项工程，甲队独做15天完成，乙队独做比甲队少5天完成，甲队做了若干天后乙队加入，又用了2天才完成，甲队先做了几天？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</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">(1/6) * 2</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) / (1/15)</gadget>
<output>10</output>

<result>10</result>