If 20% of the number of people in class A is transferred to class B, the number of people in the two classes will be equal. How much is the number of people in class B smaller than that of class A?
把甲班人数的20%调入乙班，则两班人数相等，原来乙班人数比甲班少多少
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5) - (1/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 1</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>