Donghua Primary School has 220 students in the middle grades, the upper grades are more (1/4) than the middle grades, and less (1/6) than the lower grades. How many students are there in the lower grades?
东华小学中年级有学生220名，高年级比中年级多(1/4)，而比低年级少(1/6)，低年级有学生多少人？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(5/4) / (5/6)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">220 * (3/2)</gadget>
<output>330</output>

<result>330</result>