If the length of a rectangle is increased by 25%, how much should the width be reduced in order to keep the area constant?
一个长方形的长增加25%，要想面积保持不变，宽应该减少多少
<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1 / (5/4)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>