There is oil in the bottle. After pouring in 500 grams of oil, half of it is poured out, and another 600 grams are poured in. At this time, there are 1300 grams of oil in the bottle. How much oil is in the bottle?
瓶内装有油，倒进500克油以后又倒出一半，又倒进600克，这时瓶内有油1300克，问瓶内原有油多少克？
<gadget id="calculator">1_300 - 600</gadget>
<output>700</output>

<gadget id="calculator">700 * 2</gadget>
<output>1_400</output>

<gadget id="calculator">1_400 - 500</gadget>
<output>900</output>

<result>900</result>