If you drink 2 liters of a 20-liter glass of pure milk and fill it up with water, what is the concentration of the milk?
把一杯20升的纯牛奶喝掉2升，再用水填满，则牛奶的浓度为多少
<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<gadget id="calculator">18 / 20</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">(9/10) * 1</gadget>
<output>9/10 = around 0.9</output>

<result>9/10 = around 0.9</result>