The average number of students in the six grades of the school is 200, and the ratio of the number of students in the lower, middle and upper grades is 3:4:5. How many students are there in the lower grades?
学校6个年级的平均人数是200人，而低、中、高年级的人数之比为3：4：5，低年级有多少人．
<gadget id="calculator">200 * 6</gadget>
<output>1_200</output>

<gadget id="calculator">3 + 4 + 5</gadget>
<output>12</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1_200 * (1/4)</gadget>
<output>300</output>

<result>300</result>