Add 5 kilograms of table salt to a bucket of 10% salt water. After dissolving, the concentration of salt water in the bucket increases to 20%. How many kilograms of salt are there in the bucket?
在一桶含盐10%的盐水中加进5千克食盐，溶解后，桶中盐水的浓度增加到20%，桶中原来有多少千克盐？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) / (9/10)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/4) - (1/9)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">5 / (5/36)</gadget>
<output>36</output>

<gadget id="calculator">36 * (1/9)</gadget>
<output>4</output>

<result>4</result>