Xiaoming traveled to Beijing with his parents in the summer vacation. They took a photo with everyone in the tour group. A total of 15 photos were taken. How many people participated in the tour group?
小明暑假和父母去北京旅游，他们和旅游团的每一个人合照一次像，一共照了15张照片，参加旅游团的共有多少人？
<gadget id="calculator">3 + 15</gadget>
<output>18</output>

<result>18</result>