A cup of water with the cup weighs 700 grams. After drinking half a cup of water, weigh it. The cup weighs 400 grams. How much does the cup weigh?
一杯水连杯子重700克，喝了半杯水后再称，连杯子重400克，这个杯子重多少克．
<gadget id="calculator">700 - 400</gadget>
<output>300</output>

<gadget id="calculator">300 * 2</gadget>
<output>600</output>

<gadget id="calculator">700 - 600</gadget>
<output>100</output>

<result>100</result>