There are 500 kilograms of brine with a salt content of 10%, how many kilograms of salt should be added to increase its concentration to 20%?
现有含盐10%的盐水500千克，要将它的浓度提高到20%，需加盐多少千克？
<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">500 * (9/10)</gadget>
<output>450</output>

<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">450 / (4/5)</gadget>
<output>1_125/2 = around 562.5</output>

<gadget id="calculator">(1_125/2) - 500</gadget>
<output>125/2 = around 62.5</output>

<result>125/2 = around 62.5</result>