Class 6 (A) has 56 students, 29 boys, 27 girls, 32 students participated in the Mathematical Olympiad group, 28 students participated in the science and technology group, 20 students did not participate in both groups, and 20 students participated in both groups. how many people.
六(甲)班有56名学生，男生29人，女生27人，参加奥数小组有32人，参加科技小组有28人，两个小组都没有参加的有20人，两个小组都参加的有多少人．
<gadget id="calculator">56 - 20</gadget>
<output>36</output>

<gadget id="calculator">28 - 36</gadget>
<output>-8</output>

<gadget id="calculator">32 + (-8)</gadget>
<output>24</output>

<result>24</result>