After a certain product is purchased, the retail price is set at 900 yuan per piece. In order to adapt to market competition, the store cuts the price by 10% off the retail price and sells it at a profit of 40 yuan. It can still make a profit of 10% (relative to the purchase price). Ask this question How much is the purchase price of this commodity?
某种商品进货后，零售价定为每件900元，为了适应市场竞争，商店按零售价的九折降价，并让利40元销售，仍可获利10%(相对于进价)，问这种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">900 * (9/10)</gadget>
<output>810</output>

<gadget id="calculator">810 - 40</gadget>
<output>770</output>

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

<gadget id="calculator">1 + (1/10)</gadget>
<output>11/10 = around 1.1</output>

<gadget id="calculator">770 / (11/10)</gadget>
<output>700</output>

<result>700</result>