A barrel filled with oil weighs 500 grams in total. After using up half of the oil, the barrel weighed 275 grams. How many grams does the oil weigh?
一只油桶里装满油后连桶共重500克．用掉一半油后，连桶称重275克．油重多少克？
<gadget id="calculator">500 - 275</gadget>
<output>225</output>

<gadget id="calculator">225 * 2</gadget>
<output>450</output>

<result>450</result>