Girls in the sixth grade of a school account for 4/7 of the whole grade, and there are 20 more boys than girls (2/3). How many students are there in the sixth grade?
某校六年级女生占全年级人数的(4/7)，男生比女生人数的(2/3)多20人，六年级有学生多少人？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(4/7) * (2/3)</gadget>
<output>8/21 = around 0.380952</output>

<gadget id="calculator">1 - (4/7) - (8/21)</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">20 / (1/21)</gadget>
<output>420</output>

<result>420</result>