The stationery store bought 100 pens at a price of 4 yuan each, and sold them at a price of 6 yuan each. After selling part of the pens according to the price, the rest was sold at a 10% discount. After the sale, the store made a total profit of 188 yuan. How many pens are there for the 10% discount?
文具商店以每支4元的价格进了100支钢笔，卖出时每支的标价是6元，当按标价卖出一部分后，剩余的打九折出售，卖完后商店共赢利188元，打九折的钢笔有多少支？
<gadget id="calculator">100 * 6</gadget>
<output>600</output>

<gadget id="calculator">100 * 4</gadget>
<output>400</output>

<gadget id="calculator">600 - 400 - 188</gadget>
<output>12</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">6 * (9/10)</gadget>
<output>27/5 = around 5.4</output>

<gadget id="calculator">4 - 4 - (27/5)</gadget>
<output>-27/5 = around -5.4</output>

<gadget id="calculator">6 + (-27/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">12 / (3/5)</gadget>
<output>20</output>

<result>20</result>