After adding 80 grams of water to a bottle of 100 grams of alcohol solution and diluting it into a new solution with a concentration of 40%, what is the concentration of the original solution?
一瓶100克的酒精溶液加入80克水后，稀释成浓度为40%的新溶液，原溶液的浓度是多少？
<gadget id="calculator">100 + 80</gadget>
<output>180</output>

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

<gadget id="calculator">180 * (2/5)</gadget>
<output>72</output>

<gadget id="calculator">72 / 100</gadget>
<output>18/25 = around 0.72</output>

<result>18/25 = around 0.72</result>