The students participated in the summer swimming training. There were 21 people in the lower grades who participated in the training, and the number of people in the upper grades who participated in the training was 11 times that of the lower grades. How many people participated in the training?
同学们参加暑期的游泳培训，低年级参加培训的有21人，高年级参加培训的人数是低年级的11倍．参加培训的人数一共有多少人？
<gadget id="calculator">21 * 11</gadget>
<output>231</output>

<gadget id="calculator">231 + 21</gadget>
<output>252</output>

<result>252</result>