Uncle Wang, a professional pig farmer, said: "If you sell 75 pigs, then the feed can last for 20 days. If you buy 100 pigs, then the feed can only last for 15 days." Question: How many pigs did Uncle Wang raise in total?
养猪专业户王大伯说："如果卖掉75头猪，那么饲料可维持20天，如果买进100头猪，那么饲料只能维持15天．"问：王大伯一共养了多少头猪？
<gadget id="calculator">20 * 75</gadget>
<output>1_500</output>

<gadget id="calculator">15 * 100</gadget>
<output>1_500</output>

<gadget id="calculator">1_500 + 1_500</gadget>
<output>3_000</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">3_000 / 5</gadget>
<output>600</output>

<result>600</result>