Yuying Primary School has 120 students in the upper grades, 130 students in the middle grades, and 140 students in the lower grades. What percentage of the students in the middle grades account for the whole school?
育英小学高年级有学生120人，中年级有学生130人，低年级有学生140人，中年级人数占全校人数的几分之几？
<gadget id="calculator">120 + 130 + 140</gadget>
<output>390</output>

<gadget id="calculator">130 / 390</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>