There are 520 geese in a farm, and the number of ducks is 200 less than twice that of geese. How many ducks are there?
某养殖场有鹅520只，鸭的只数比鹅的2倍少200只，鸭有多少只？
<gadget id="calculator">520 * 2</gadget>
<output>1_040</output>

<gadget id="calculator">1_040 - 200</gadget>
<output>840</output>

<result>840</result>