Class 31 has 20 people participating in the calligraphy interest group, 13 people participating in the English interest group, and 7 people participating in both interest groups. How many people are there in the two interest groups?
三1班参加书法兴趣小组的有20人，参加英语兴趣小组的有13人，两个兴趣小组都参加的有7人，两个兴趣小组共有多少人．
<gadget id="calculator">13 - 7</gadget>
<output>6</output>

<gadget id="calculator">20 + 6</gadget>
<output>26</output>

<result>26</result>