product is sold at a reduced price according to the season. If the current price is reduced by 10%, a profit of 180 yuan can still be made; if the price is reduced by 20%, the loss will be 240 yuan. What is the purchase price of this commodity?
一件商品随季节变化降价出售，如果按现价降价10%，仍可获利180元；如果降价20%就要亏损240元，这种商品的进价是多少元？
<gadget id="calculator">180 + 240</gadget>
<output>420</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(9/10) - (4/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">420 / (1/10)</gadget>
<output>4_200</output>

<gadget id="calculator">4_200 * (9/10)</gadget>
<output>3_780</output>

<gadget id="calculator">3_780 - 180</gadget>
<output>3_600</output>

<result>3_600</result>