25 people from Class 1 participated in the Chinese and Mathematics Interest Group. There are 15 people participating in the Chinese interest group, 18 people participating in the mathematics interest group, and how many people participate in both the language and mathematics interest groups.
六1班有25人参加了语文和数学兴趣小组．参加语文兴趣小组的有15人，参加数学兴趣小组的有18人，语数兴趣小组都参加的有多少人．
<gadget id="calculator">18 + 15</gadget>
<output>33</output>

<gadget id="calculator">33 - 25</gadget>
<output>8</output>

<result>8</result>