(1/5) of the students in the experimental primary school participated in the extracurricular interest group, and later 20 students joined the extracurricular interest group voluntarily. At this time, the number of participants in the extracurricular interest group accounted for (1/3). How many students participated in the extracurricular interest group?
实验小学有(1/5)的学生参加了课外兴趣小组，后来又有20名同学主动加入课外兴趣小组，这时参加课外兴趣小组的人数占没参加人数的(1/3)．原来有多少名同学参加了课外兴趣小组．
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">20 / (1/20)</gadget>
<output>400</output>

<gadget id="calculator">400 * (1/5)</gadget>
<output>80</output>

<result>80</result>