The two cups are respectively filled with 40% and 20% salt water, pour them together and mix them into 25% salt water, if you add 200 grams of 35% salt water, the concentration becomes 30%. So how many grams of the original 40% salt water.
两个杯中分别装有40%与20%的食盐水，倒在一起后混合成浓度为25%食盐水，若再加入200克35%的食盐水，则浓度变为30%．那么原有40%的食盐水多少克．
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">200 * (1/4)</gadget>
<output>50</output>

<result>50</result>