There is 1 kg of salt water containing 40 grams of salt, and salt is added to make it a salt water with a concentration of not less than 20%, how many grams of salt should be added?
有1千克含40克食盐的盐水，再加入食盐，使它成为浓度不小于20%的食盐水，应加入多少克食盐？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 1_000</gadget>
<output>200</output>

<gadget id="calculator">200 - 40</gadget>
<output>160</output>

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

<gadget id="calculator">160 / (4/5)</gadget>
<output>200</output>

<result>200</result>