Class 2, Grade 6, collected used beverage bottles. Among them, the students in Group A collected 17 on average, the students in Group B collected 20 on average, and the students in Group C collected 21 on average. If the three groups have collected 233 used beverage bottles, how many students are there in the three groups?
六年级2班的同学收集废旧饮料瓶．其中，甲组同学平均每人收集17个，乙组同学平均每人收集20个，丙组同学平均每人收集21个．若三个小组共收集了233个废旧饮料瓶，则这三个小组共有学生多少人．
<gadget id="calculator">17 * 3</gadget>
<output>51</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<gadget id="calculator">233 - 51 - 42</gadget>
<output>140</output>

<gadget id="calculator">140 / 20</gadget>
<output>7</output>

<gadget id="calculator">3 + 7 + 2</gadget>
<output>12</output>

<result>12</result>