If a product with a price tag of 40 yuan is sold at a discount of 10% off the price, it can still make a profit of 20%, so how much is the purchase price of the product?
一个标价为40元的商品按标价的九折出售后仍可获利20%，则该商品的进价为多少元？
<gadget id="calculator">90 / 100</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>6/5 = around 1.2</output>

<gadget id="calculator">(9/10) / (6/5)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">40 * (3/4)</gadget>
<output>30</output>

<result>30</result>