There are a total of 750 roosters and hens in the chicken farm. After half of the hens are sold, there will be the same number of roosters and hens. How many hens are there in the chicken farm?
养鸡场公鸡和母鸡一共750只，卖出一半母鸡后，公鸡和母鸡的只数同样多．养鸡场原有母鸡多少只？
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">750 / 3</gadget>
<output>250</output>

<gadget id="calculator">750 - 250</gadget>
<output>500</output>

<result>500</result>