There is a cup filled with 100 grams of 40% salt water. Operate in sequence as follows: Pour out 40 grams of salt water from it. Then fill the cup with water. After three operations. What is the concentration of salt water in the glass.
现有一个装满100克浓度为40%的盐水的杯子．按如下过程依次操作：从中倒出40克盐水．再用水将杯子加满．三次操作后．杯中盐水的浓度是多少．
<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 100</gadget>
<output>1/250 = around 0.004</output>

<gadget id="calculator">60 * (1/250)</gadget>
<output>6/25 = around 0.24</output>

<gadget id="calculator">(6/25) / 100</gadget>
<output>3/1_250 = around 0.0024</output>

<gadget id="calculator">60 * (3/1_250)</gadget>
<output>18/125 = around 0.144</output>

<gadget id="calculator">(18/125) / 100</gadget>
<output>9/6_250 = around 0.00144</output>

<gadget id="calculator">60 * (9/6_250)</gadget>
<output>54/625 = around 0.0864</output>

<result>54/625 = around 0.0864</result>