The weight of a bottle of jam is 700 grams. After eating half of the jam, the weight is 400 grams. What is the weight of the bottle of jam?
一瓶果酱连瓶重700克，吃掉一半果酱后重400克，果酱瓶重多少克．
<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>