After drinking 40% of a glass of milk, fill up with water and stir, then drink 40%, how much milk is left in the glass
一杯牛奶喝去40%以后，加满水搅拌，再喝去40%，这时杯中牛奶还剩多少
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) * (3/5)</gadget>
<output>9/25 = around 0.36</output>

<result>9/25 = around 0.36</result>