Students from class 3 and 3 participated in the sports meeting, 20 students participated in the relay race, 15 students participated in the rope skipping, and 8 students participated in both competitions. How many people in Class 3 and 3 participated in these two competitions?
三3班同学参加运动会，参加接力赛的有20名同学，参加跳绳的有15名同学，两种比赛都参加了的有8人．三3班参加这两项比赛的共有多少人．
<gadget id="calculator">15 - 8</gadget>
<output>7</output>

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

<result>27</result>