There are several grams of 5% brine, and after evaporating some water, it becomes 10% brine, and then 300 grams of 5% brine is added and mixed to become 7.5% brine. Q: How many grams was the initial brine?
有若干克5%的盐水，蒸发了一些水分后变成了10%的盐水，再加入300克5%的盐水混合后变为7.5%的盐水．问：最初的盐水是多少克？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">300 * (1/10)</gadget>
<output>30</output>

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

<gadget id="calculator">30 / (1/20)</gadget>
<output>600</output>

<result>600</result>