A cup is filled with water, and the total is 500 grams, and half of the water is poured out, and the total is 300 grams. How much does this cup weigh in grams?
一个杯子里装满了水，连杯称一共500克，倒掉水的一半，连杯称一共300克．这只杯子重多少克．
<gadget id="calculator">500 - 300</gadget>
<output>200</output>

<gadget id="calculator">300 - 200</gadget>
<output>100</output>

<result>100</result>