The two cups are filled with 40% and 10% salt water respectively, and the concentration of the mixed salt water is 30% after being poured together. If 300 grams of 20% salt water is added, the concentration becomes 25%. So how many grams of the original 40% salt water.
两个杯中分别装有浓度40%与10%的食盐水，倒在一起后混合食盐水浓度为30%．若再加入300克20%的食盐水，则浓度变为25%．那么原有40%的食盐水多少克．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(3/10) - (1/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) / (1/10)</gadget>
<output>2</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">300 * (2/3)</gadget>
<output>200</output>

<result>200</result>