There are 320 students in the upper grades of a certain elementary school, accounting for 1/4 of the total number of students in the school, and 20% of the students in the lower grades. How many students are there in the lower grades?
某小学高年级有320人，占全校总人数(1/4)，低年级是全校人数的20%，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">320 / (1/4)</gadget>
<output>1_280</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1_280 * (1/5)</gadget>
<output>256</output>

<result>256</result>