A professional poultry farmer raises 980 chickens, 20 chickens twice as many as ducks. How many ducks do you have?
一个养禽专业户养鸡980只，养的鸡比鸭的2倍多20只．养鸭多少只？
<gadget id="calculator">980 - 20</gadget>
<output>960</output>

<gadget id="calculator">960 / 2</gadget>
<output>480</output>

<result>480</result>