It's the Chinese New Year, and the students have to make some handicrafts for the elderly in the nursing home. At the beginning, the students in the art group did it for one day, and then 15 more students worked with them for another two days, and it was just finished. Assume that each student has the same work efficiency, and it takes 60 days for a student to complete alone. So how many students are there in the art group?
过年了，同学们要亲手做一些工艺品送给敬老院的老人．开始时艺术小组的同学们先做一天，随后增加15位同学和他们一起又做了两天，恰好完成．假设每位同学的工作效率相同，且一位同学单独完成需要60天．那么艺术小组的同学有多少位．
<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/60) * 2 * 15</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/60) * 2</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/60) + (1/30)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/2) / (1/20)</gadget>
<output>10</output>

<result>10</result>