There are 45 people in the May 1st class, of which 20 people participated in ball games, 10 people participated in track and field sports, and only 3 people participated in ball games and track and field sports. Then, how many people did not participate in these two sports? people?
五一班有45人，其中有20人参加了球类运动，10人参加了田径运动，只有3人及参加了球类运动又参加了田径运动，那么，没有参加这两种运动的有多少人？
<gadget id="calculator">10 - 3</gadget>
<output>7</output>

<gadget id="calculator">20 + 7</gadget>
<output>27</output>

<gadget id="calculator">45 - 27</gadget>
<output>18</output>

<result>18</result>