During the "May 1st" Labor Day, the school organized fifth and sixth graders to watch educational videos. A total of 680 people went there. Among them, the number of fifth graders was 1.5 times that of sixth graders, 20 people less. How many people went to sixth graders?
"五一"劳动节期间，学校组织五、六年级的同学观看教育影片，一共去了680人，其中五年级人数是六年级人数的1.5倍少20人，六年级去了多少人？
<gadget id="calculator">680 + 20</gadget>
<output>700</output>

<gadget id="calculator">1 + 1.5</gadget>
<output>2.5</output>

<gadget id="calculator">700 / 2.5</gadget>
<output>280</output>

<gadget id="calculator">680 - 280</gadget>
<output>400</output>

<result>400</result>