Xiao Ming helped his mother sell goods. On the first day, he sold 10 items at a profit of 11 yuan. On the second day, during the May Day holiday, the price was reduced. After a while, he sold 11 items at a profit of 5 yuan. The total price is exactly the same as the total price of 10 sold yesterday. How much is the purchase price of this commodity.
小明帮妈妈卖商品，第一天按11元的利润卖出10个，第二个正值五一假期，降价优惠，不一会就以5元的利润卖出11个，结果这11个的总价正好与昨天卖出10个的总价相同．这种商品的进价是多少元．
<gadget id="calculator">11 * 10</gadget>
<output>110</output>

<gadget id="calculator">11 * 5</gadget>
<output>55</output>

<gadget id="calculator">110 - 55</gadget>
<output>55</output>

<gadget id="calculator">11 - 10</gadget>
<output>1</output>

<gadget id="calculator">55 / 1</gadget>
<output>55</output>

<result>55</result>