How many kilograms of salt can be added to 20 kg of salt water containing 15% salt to make the concentration of the salt water 20%.
在含盐15%的20千克盐水中，加多少千克的盐，就能使盐水的浓度是20%．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">20 * (17/20)</gadget>
<output>17</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">17 / (4/5)</gadget>
<output>85/4 = around 21.25</output>

<gadget id="calculator">(85/4) - 20</gadget>
<output>5/4 = around 1.25</output>

<result>5/4 = around 1.25</result>