If the same 3 small cups of water are poured into an empty jug, the weight of the jug is 800 grams. If such 5 small cups of water are poured into the empty jug, the weight of the jug is 1 kg. How much does the empty jug weigh in grams?
如果往一个空水壶中倒入同样的3小杯水后，连壶重800克，如果往这个空水壶中倒入这样的5小杯水后，连壶重1千克．这个空水壶重多少克．
<gadget id="calculator">200 / 2</gadget>
<output>100</output>

<gadget id="calculator">100 * 3</gadget>
<output>300</output>

<gadget id="calculator">800 - 300</gadget>
<output>500</output>

<result>500</result>