A glass of milk weighs 750 grams in total. After drinking half of it, the weight of the glass is 500 grams. What is the net weight of this glass of milk?
一杯牛奶连杯共重750克，喝掉一半后连杯共重500克，这杯牛奶净重多少克？
<gadget id="calculator">750 - 500</gadget>
<output>250</output>

<gadget id="calculator">250 * 2</gadget>
<output>500</output>

<result>500</result>