The number of fifth grade students in the experimental primary school is 1.2 times the number of fourth grade students. If the fourth grade students transfer 20 more students, there will be the same number of students in the two grades. How many students are there in the original fourth grade.
实验小学五年级人数是四年级学生人数的1.2倍，如果四年级学生再转来20人，则两个年级学生就一样多，原来四年级有多少人．
<gadget id="calculator">1.2 - 1</gadget>
<output>0.2</output>

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

<result>100</result>