A certain commodity is sold at the original price, and the profit per piece is 20% of the cost. Later, it is sold at 90% of the original price. As a result, the number of pieces sold per day increases by 2.5 times compared with that before the price reduction. How much has been increased.
某商品按原定价出售，每件利润是成本的20%，后来按原定价的90%出售，结果每天售出的件数比降件前增加了2.5倍，每天经营这种商品的总利润比降价前增加了多少．
<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">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(6/5) * (9/10)</gadget>
<output>27/25 = around 1.08</output>

<gadget id="calculator">(27/25) - 1</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">2.5 + 1</gadget>
<output>3.5</output>

<gadget id="calculator">(2/25) * 3.5</gadget>
<output>0.28</output>

<gadget id="calculator">0.28 - 0.2</gadget>
<output>0.08</output>

<gadget id="calculator">0.08 / 0.2</gadget>
<output>0.4</output>

<result>0.4</result>