How many grams of water should be added to 50 grams of salt water containing 20% salt to make the salt water contain 5% salt.
含盐20%的盐水50克，再加多少克水，才能使盐水含盐5%．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/5) / (1/20)</gadget>
<output>4</output>

<gadget id="calculator">50 * 4</gadget>
<output>200</output>

<gadget id="calculator">200 - 50</gadget>
<output>150</output>

<result>150</result>