A commodity is priced at a 20% profit, and then sold at a 10% discount, earning a profit of 40 yuan. What is the cost price of this item?
一件商品按20%的利润定价，然后以九折卖出，获得利润40元．这件商品的成本价是多少元？
<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">40 / (2/25)</gadget>
<output>500</output>

<result>500</result>