There are 280 grams of brine with a salt content of 20%, and now to make these brines into brine with a salt content of 8%, how many grams of water should be added to it?
有含盐率20%的盐水280克，现要把这些盐水配制成含盐率为8%的盐水，需要向里面加水多少克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">8 / 100</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">(1/5) / (2/25)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">280 * (5/2)</gadget>
<output>700</output>

<gadget id="calculator">700 - 280</gadget>
<output>420</output>

<result>420</result>