If the daily sales volume of a certain product decreases by 20% after the price increase, but the sales volume increases by 20%, what is the percentage of the price increase?
某种商品，提价后每天销量比原来减少20%，销售额却比原来增加了20%，说明提价的百分数为多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

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

<gadget id="calculator">(6/5) / (4/5)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) - 1</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>