There are 50 kilograms of salt water with 12% salt content, how many kilograms of salt should be added to make the salt water with 20% salt content.
有含盐12%的盐水50千克，要使盐水含盐20%，需要加盐多少千克．
<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">1 - (3/25)</gadget>
<output>22/25 = around 0.88</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">(22/25) / (4/5)</gadget>
<output>11/10 = around 1.1</output>

<gadget id="calculator">50 * (11/10)</gadget>
<output>55</output>

<gadget id="calculator">55 - 50</gadget>
<output>5</output>

<result>5</result>