Donghua Primary School has 520 students in the middle grades, the upper grades are more (1/3) than the middle grades, and less (1/3) than the lower grades. How many students are there in the lower grades?
东华小学中年级有学生520名，高年级比中年级多(1/3)，而比低年级少(1/3)，低年级有学生多少人？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + (1/3)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">520 / (4/3) / (2/3)</gadget>
<output>585</output>

<result>585</result>