For a glass bottle filled with chocolate beans, the mass of the empty bottle accounts for 20% of the total mass of the glass bottle filled with chocolate beans. What percentage is the quality of the original chocolate beans?
装满巧克力豆的玻璃瓶，空瓶质量占装满巧克力豆的玻璃瓶总质量20%，倒出一部分巧克力豆后，倒出的质量是原来总质量的40%，则剩下的巧克力豆的质量是原来巧克力豆的百分之几？
<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">1 * (3/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 * (1/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(3/5) - (1/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(2/5) / (4/5)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>