A bottle of oil weighs 670 grams. After half of it is poured out, it still weighs 420 grams. How many grams does this oil bottle weigh?
一瓶油连瓶重670克，倒出一半后，还重420克，这个油瓶重多少克？
<gadget id="calculator">670 - 420</gadget>
<output>250</output>

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

<gadget id="calculator">670 - 500</gadget>
<output>170</output>

<result>170</result>