There are 320 students in the upper grades of a certain elementary school, accounting for 4/9 of the total number of students in the school, and 25% 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，占全校总人数的(4/9)，低年级是全校人数的25%，低年级有学生多少人？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">320 / (4/9)</gadget>
<output>720</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">720 * (1/4)</gadget>
<output>180</output>

<result>180</result>