There are 320 students in the sixth grade in a certain school, exactly the number of fifth grade students (4/5), and the number of fifth grade students is the fourth grade (8/7), how many students are there in the fourth and fifth grades?
某校六年级有320人，正好是五年级人数的(4/5)，而五年级学生的人数是四年级的(8/7)，四、五年级一共有多少人？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">320 / (4/5)</gadget>
<output>400</output>

<gadget id="calculator">8 / 7</gadget>
<output>8/7 = around 1.142857</output>

<gadget id="calculator">320 / (4/5) / (8/7)</gadget>
<output>350</output>

<gadget id="calculator">400 + 350</gadget>
<output>750</output>

<result>750</result>