There are 45 students in a class, and 15 students participated in extracurricular interest groups, which accounted for the number of students who did not participate in the interest groups.
某班学生共45人，有15名学生参加了课外兴趣小组，占没有参加兴趣小组学生数的多少．
<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<gadget id="calculator">15 / 30</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>