There are 450 students in the second grade, and 9 classes in the third grade, each class has 45 students. How many people are there in the second and third grades?
二年级有450人，三年级有9个班，每个班有45人．二、三年级一共有多少人？
<gadget id="calculator">45 * 9</gadget>
<output>405</output>

<gadget id="calculator">405 + 450</gadget>
<output>855</output>

<result>855</result>